CN116868623A

CN116868623A - Communication system and base station

Info

Publication number: CN116868623A
Application number: CN202280015955.7A
Authority: CN
Inventors: 望月满; 下田忠宏
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2021-02-25
Filing date: 2022-02-21
Publication date: 2023-10-10
Also published as: JPWO2022181526A1; KR20230147612A; WO2022181526A1; EP4301045A1; US20240129820A1

Abstract

In order to improve communication quality in a communication system using inter-terminal communication, the communication system of the present invention includes: a 1 st base station (S-gNB) to which a 1 st communication terminal (Remote UE) is connected, the 1 st communication terminal supporting inter-terminal communication in which communication terminals directly communicate with each other; and a 2 nd base station (T-gNB) to which a 2 nd communication terminal (Relay UE) is connected, the 2 nd communication terminal supporting inter-terminal communication, wherein when a request for switching a 1 st communication terminal to connect to the base station via the 2 nd communication terminal is received, the 2 nd base station transmits communication setting information indicating setting contents for inter-terminal communication between the 1 st communication terminal and the 2 nd communication terminal to the 1 st communication terminal and the 2 nd communication terminal.

Description

Communication system and base station

Technical Field

The present disclosure relates to wireless communication technology.

Background

In 3GPP (3 rd Generation Partnership Project, third generation partnership project), which is a standardization organization of a mobile communication system, a communication scheme called long term evolution (Long Term Evolution:lte) in a radio section and a system architecture evolution (System Architecture Evolution:sae) in a system overall configuration including a core network and a radio access network (hereinafter, also referred to as a network) has been studied (for example, non-patent documents 1 to 5). This communication scheme is also known as a 3.9G (3.9 generation:3.9 generation) system.

As an access scheme for LTE, OFDM (Orthogonal Frequency Division Multiplexing: orthogonal frequency division multiplexing) is used in the downlink direction, and SC-FDMA (Single Carrier Frequency Division Multiple Access: single carrier frequency division multiple access) is used in the uplink direction. Unlike W-CDMA (Wideband Code Division Multiple Access: wideband code division multiple access), LTE does not include circuit switching, but is a packet communication scheme.

A decision about the frame structure of the LTE system in 3GPP described in non-patent document 1 (chapter 5) will be described with reference to fig. 1. Fig. 1 is an explanatory diagram showing a configuration of a radio frame used in a communication system of the LTE scheme. In fig. 1, one Radio frame (Radio frame) is 10ms. The radio frame is divided into 10 subframes (subframes) of equal size. The subframe is divided into 2 equal-sized slots (slots). The first and sixth subframes of each radio frame contain downlink synchronization signals (Downlink Synchronization Signal). Among the synchronization signals are a first synchronization signal (Primary Synchronization Signal) (primary synchronization signal): P-SS) and a second synchronization signal (Secondary Synchronization Signal) (secondary synchronization signal): S-SS).

Non-patent document 1 (chapter five) describes a decision about a channel structure in the LTE system in 3 GPP. It is assumed that the same channel structure as that of the non-CSG cell is also used in the CSG (Closed Subscriber Group: closed subscriber group) cell.

The physical broadcast channel (Physical Broadcast Channel: PBCH) is a downlink transmission channel from a base station apparatus (hereinafter, abbreviated as "base station") to a communication terminal apparatus (hereinafter, abbreviated as "communication terminal") such as a mobile terminal apparatus (hereinafter, abbreviated as "mobile terminal"). The BCH transport block (transport block) is mapped to four subframes in a 40ms interval. There is no clear signaling of 40ms timing.

The physical control format indicator channel (Physical Control Format Indicator Channel: PCFICH) is a downlink transmission channel from the base station to the communication terminal. The PCFICH notifies the communication terminal of the number of OFDM (Orthogonal Frequency Division Multiplexing: orthogonal frequency division multiplexing) symbols for PDCCHs from the base station. The PCFICH is transmitted for each subframe.

The physical downlink control channel (Physical Downlink Control Channel: PDCCH) is a downlink transmission channel from the base station to the communication terminal. The PDCCH notifies resource allocation (allocation) information of a downlink shared Channel (Downlink Shared Channel: DL-SCH) which is one of the transport channels to be described later, resource allocation (allocation) information of a Paging Channel (PCH) which is one of the transport channels to be described later, and HARQ (Hybrid Automatic Repeat reQuest: hybrid automatic repeat request) information related to the DL-SCH. The PDCCH transmits an uplink scheduling grant (Uplink Scheduling Grant). The PDCCH transmits Ack (Acknowledgement)/Nack (Negative Acknowledgement: unacknowledged) which is a response signal to uplink transmission. The PDCCH is also referred to as an L1/L2 control signal.

The physical downlink shared channel (Physical Downlink Shared Channel: PDSCH) is a downlink transmission channel from the base station to the communication terminal. The PDSCH is mapped with a downlink shared channel (DL-SCH) as a transport channel and a PCH as a transport channel.

The physical multicast channel (Physical Multicast Channel: PMCH) is a downlink transmission channel from the base station to the communication terminal. The PMCH has a multicast channel (Multicast Channel: MCH) mapped thereto as a transport channel.

The physical uplink control channel (Physical Uplink Control Channel: PUCCH) is an uplink transmission channel from the communication terminal to the base station. The PUCCH transmits a response signal (response signal) for downlink transmission, i.e., ack/Nack. The PUCCH transmits CSI (Channel State Information: channel state information). The CSI is composed of RI (Rank Indicator: rank indication), PMI (Precoding Matrix Indicator: precoding matrix indication), CQI (Channel Quality Indicator: channel quality Indicator) report. RI refers to rank information of a channel matrix of MIMO. The PMI is information of a precoding wait matrix used for MIMO. CQI is quality information indicating the quality of received data or indicating the quality of a communication line. And PUCCH transmits a scheduling request (Scheduling Request: SR).

The physical uplink shared channel (Physical Uplink Shared Channel: PUSCH) is an uplink transmission channel from the communication terminal to the base station. The PUSCH has an uplink shared channel (Uplink Shared Channel: UL-SCH) mapped thereon as one of the transport channels.

The physical HARQ indicator channel (Physical Hybrid ARQ Indicator Channel: PHICH) is a downlink transmission channel from the base station to the communication terminal. The PHICH transmits a response signal for uplink transmission, ack/Nack. The physical random access channel (Physical Random Access Channel: PRACH) is an uplink transmission channel from the communication terminal to the base station. The PRACH transmits a random access preamble (random access preamble).

A downlink Reference Signal (RS) is a symbol known as a communication system of the LTE scheme. The following 5 downlink reference signals are defined. Cell-specific reference signals (Cell-specific Reference Signal: CRS), MBSFN reference signals (MBSFN Reference Signal), data demodulation reference signals (Demodulation Reference Signal: DM-RS) which are UE-specific reference signals (UE-specific Reference Signal), positioning reference signals (Positioning Reference Signal: PRS), and channel state information reference signals (Channel State Information Reference Signal: CSI-RS). As measurement of the physical layer of the communication terminal, there is measurement of the received power (Reference Signal Received Power:rsrp) of the reference signal.

The uplink reference signal is also a symbol known as a communication system of the LTE scheme. The following 2 uplink reference signals are defined. Reference signals for data demodulation (Demodulation Reference Signal: DM-RS) and reference signals for detection (Sounding Reference Signal: SRS).

A transmission channel (Transport Channel) described in non-patent document 1 (chapter 5) is described. The broadcast channel (Broadcast Channel: BCH) of the downlink transport channels is broadcast to the entire coverage of its base station (cell). The BCH is mapped to a Physical Broadcast Channel (PBCH).

HARQ (Hybrid ARQ) based retransmission control is applied to the downlink shared channel (Downlink Shared Channel: DL-SCH). The DL-SCH can be broadcast to the entire coverage of a base station (cell). The DL-SCH supports dynamic or quasi-static (Semi-static) resource allocation. Quasi-static resource allocation is also referred to as persistent scheduling (Persistent Scheduling). The DL-SCH supports discontinuous reception (Discontinuous reception: DRX) of the communication terminal in order to reduce power consumption of the communication terminal. The DL-SCH is mapped to a Physical Downlink Shared Channel (PDSCH).

The Paging Channel (PCH) supports DRX of the communication terminal in order to reduce power consumption of the communication terminal. The PCH is required to be broadcast to the entire coverage area of the base station (cell). The PCH is mapped to a physical resource such as a Physical Downlink Shared Channel (PDSCH) that can be dynamically utilized for traffic (traffic).

The multicast channel (Multicast Channel: MCH) is used for broadcasting to the whole coverage of the base station (cell). The MCH supports SFN synthesis of MBMS (Multimedia Broadcast Multicast Service: multimedia broadcast multicast service) services (MTCH and MCCH) in multi-cell transmission. The MCH is supported in terms of static resource allocation. The MCH is mapped to the PMCH.

Retransmission control based on HARQ (Hybrid ARQ) is applied to an uplink shared channel (Uplink Shared Channel: UL-SCH) among uplink transport channels. The UL-SCH supports dynamic or quasi-static (Semi-static) resource allocation. The UL-SCH is mapped to a Physical Uplink Shared Channel (PUSCH).

The random access channel (Random Access Channel: RACH) is limited to control information. RACH presents a risk of collision. The RACH is mapped to a Physical Random Access Channel (PRACH).

HARQ will be described. HARQ is a technique for improving the communication quality of a transmission line by combining an automatic retransmission request (Automatic Repeat reQuest: ARQ) and error correction (Forward Error Correction: forward error correction). HARQ has the following advantages: even for a transmission line in which communication quality is changed, error correction can be effectively performed by retransmission. In particular, in the case of retransmission, the quality can be further improved by combining the reception result of the primary transmission and the reception result of the retransmission.

An example of a retransmission method is described. When the reception side cannot decode the received data correctly, in other words, when a CRC (Cyclic Redundancy Check: cyclic redundancy check) error is generated (crc=ng), the reception side transmits "Nack" to the transmission side. The transmitting side that receives "Nack" retransmits the data. When the reception side can correctly decode the reception data, in other words, when no CRC error is generated (crc=ok), the reception side transmits "Ack" to the transmission side. The transmitting side that receives the "Ack" transmits the next data.

A Logical Channel (Logical Channel) described in non-patent document 1 (chapter 6) is described. The broadcast control channel (Broadcast Control Channel: BCCH) is a downlink channel for broadcasting system control information. The BCCH, which is a logical channel, is mapped to a Broadcast Channel (BCH), which is a transport channel, or a downlink shared channel (DL-SCH).

The paging control channel (Paging Control Channel: PCCH) is a downlink channel for transmitting a change of paging information (Paging Information) and system information (System Information). PCCH is used in cases where the network is not aware of the cell location of the communication terminal. PCCH, which is a logical channel, is mapped to a Paging Channel (PCH), which is a transport channel.

The shared control channel (Common Control Channel: CCCH) is a channel for transmitting control information between the communication terminal and the base station. CCCH is used in cases where there is no RRC connection (connection) between the communication terminal and the network. In the downlink direction, the CCCH is mapped to a downlink shared channel (DL-SCH) as a transport channel. In the uplink direction, the CCCH is mapped to an uplink shared channel (UL-SCH) as a transport channel.

The multicast control channel (Multicast Control Channel: MCCH) is a downlink channel for point-to-multipoint transmission. The MCCH is used to transmit MBMS control information for one or several MTCHs from a network to a communication terminal. The MCCH is only used for communication terminals in the MBMS reception procedure. The MCCH is mapped to a Multicast Channel (MCH) as a transport channel.

The dedicated control channel (Dedicated Control Channel: DCCH) is a channel for transmitting dedicated control information between the communication terminal and the network in a point-to-point manner. DCCH is used in the case where the communication terminal is an RRC connection (connection). DCCH is mapped to an uplink shared channel (UL-SCH) in uplink and mapped to a downlink shared channel (DL-SCH) in downlink.

The dedicated traffic channel (Dedicated Traffic Channel: DTCH) is a channel for point-to-point communication for transmitting user information to a dedicated communication terminal. DTCH exists in both uplink and downlink. The DTCH is mapped to an uplink shared channel (UL-SCH) in the uplink and mapped to a downlink shared channel (DL-SCH) in the downlink.

The multicast traffic channel (Multicast Traffic Channel: MTCH) is a downlink channel for transmitting traffic data from the network to the communication terminals. The MTCH is a channel only for a communication terminal in the MBMS reception procedure. The MTCH is mapped to a Multicast Channel (MCH).

CGI refers to cell global identity (Cell Global Identifier). ECGI refers to E-UTRAN cell Global identity (E-UTRAN Cell Global Identifier). CSG (Closed Subscriber Group: closed subscriber group) cells are introduced in LTE, LTE-A (Long Term Evolution Advanced: long term evolution) and UMTS (Universal Mobile Telecommunication System: universal Mobile Telecommunications System) described later.

The position tracking of the communication terminal is performed in units of an area constituted by one or more cells. The position tracking is performed to enable the communication terminal to be called by tracking the position of the communication terminal even in the standby state, in other words, to enable the communication terminal to be called. The area for position tracking of the communication terminal is referred to as a tracking area.

In addition, as release 10, the standard system of long term evolution (Long Term Evolution Advanced: LTE-a) is advancing in 3GPP (see non-patent document 3 and non-patent document 4). LTE-a is based on the wireless inter-range communication scheme of LTE, and is constructed by adding some new technologies thereto.

In the LTE-a system, carrier aggregation (Carrier Aggregation: CA) in which two or more component carriers (Component Carrier: CC) are aggregated (also referred to as aggregation) is studied in order to support a wider bandwidth (transmission bandwidths) up to 100 MHz. CA is described in non-patent document 1.

In the case of constructing CA, a UE as a communication terminal has an RRC connection (RRC connection) unique to a Network (NW). In RRC connection, one serving cell provides NAS mobility information and security inputs. This Cell is referred to as a Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is a downlink primary component carrier (Downlink Primary Component Carrier: DL PCC). In the uplink, the carrier corresponding to the PCell is an uplink primary component carrier (Uplink Primary Component Carrier: UL PCC).

According to the capability (capability) of the UE, a Secondary Cell (SCell) is constructed to form a group of serving cells together with the PCell. In the downlink, the carrier corresponding to the SCell is a downlink secondary component carrier (Downlink Secondary Component Carrier: DL SCC). In the uplink, the carrier corresponding to the SCell is an uplink secondary component carrier (Uplink Secondary Component Carrier: UL SCC).

For one UE, a group of serving cells consisting of one PCell and more than one SCell is configured.

Further, as new technologies of LTE-a, there are technologies supporting a wider band (Wider bandwidth extension: bandwidth expansion), and technologies supporting multi-site coordinated transmission/reception (Coordinated Multiple Point transmission and reception: coMP), and the like. Non-patent document 1 describes CoMP studied for realizing LTE-a in 3 GPP.

In addition, in 3GPP, in order to cope with a large amount of traffic in the future, small enbs (hereinafter, sometimes referred to as "small-scale base station apparatuses") constituting small cells are being studied. For example, the following techniques and the like are being studied: by providing a plurality of small enbs and configuring a plurality of small cells, the frequency utilization efficiency is improved, and the communication capacity is increased. Specifically, there are dual connections (Dual Connectivity; abbreviated as DC) and the like in which a UE communicates with two enbs. DC is described in non-patent document 1.

One of enbs performing Dual Connectivity (DC) is sometimes referred to as a "master eNB (abbreviated MeNB)", and the other is sometimes referred to as a "secondary eNB (abbreviated SeNB)".

The traffic volume of the mobile network tends to increase, and the communication speed is also advancing to a higher speed. If LTE and LTE-a are formally started to be operated, it is expected that the communication speed will be further increased.

In addition, a fifth generation (hereinafter, sometimes referred to as "5G") wireless access system, which aims at starting service after 2020 for mobile communication in an updated generation, is under study. For example, in europe, the requirement of 5G is summarized by the metas organization (see non-patent document 5).

In the 5G radio access system, the LTE system has a system capacity of 1000 times, a data transfer rate of 100 times, a data processing delay of 1 (1/10) of 10 minutes, and a number of simultaneous connections of the communication terminals of 100 times, and it is necessary to achieve further reduction in power consumption and cost of the device.

In order to meet such a demand, 3GPP is under discussion as a standard of release 15,5G (see non-patent documents 6 to 19). The technique of the radio section of 5G is called "New Radio Access Technology: new Radio access technology "(" New Radio "is simply referred to as" NR ").

The NR system is under discussion of the LTE system and the LTE-a system, but changes and additions from the LTE system and the LTE-a system are performed in the following points.

As an access scheme for NR, OFDM is used in a downlink direction, and OFDM or DFT-s-OFDM (DFT-spread) -OFDM is used in an uplink direction.

In NR, a higher frequency can be used than in LTE to increase transmission speed and reduce processing delay.

In NR, a narrow beam-like transmission/reception range (beam forming) is formed, and the direction of a beam is changed (beam scanning), so that it is possible to ensure cell coverage.

Various subcarrier spacings, i.e., various parameter sets (Numerology), are supported in the frame structure of NR. In NR, 1 subframe is 1 ms, and 1 slot is composed of 14 symbols, regardless of a parameter set. The number of slots included in 1 subframe is one in a parameter set having a subcarrier interval of 15kHz, and the number of slots included in other parameter sets increases in proportion to the subcarrier interval (see non-patent document 13 (3GPPTS38.211)).

The downlink synchronization signal in NR is transmitted from the base station as a synchronization signal burst (Synchronization Signal Burst: hereinafter, sometimes referred to as SS burst) in a predetermined period for a predetermined duration. The SS burst is composed of a synchronization signal module (Synchronization Signal Block; hereinafter, sometimes referred to as SS module) for each beam of the base station.

The base station changes the beam for the duration of the SS burst to transmit the SS module for each beam. The SS module is composed of P-SS, S-SS and PBCH.

In NR, as a downlink reference signal of NR, by adding a phase tracking reference signal (Phase Tracking Reference Signal: PTRS), the influence of phase noise can be reduced. In the uplink reference signal, PTRS is also added in the same manner as in the downlink.

In NR, a slot configuration notification (Slot Format Indication: SFI) is added to information included in PDCCH in order to flexibly switch DL/UL in a slot.

In NR, the base station sets a Part of a carrier band (hereinafter, sometimes referred to as a Bandwidth Part (BWP)) for the UE in advance, and the UE transmits and receives between itself and the base station in the BWP, so that power consumption in the UE can be reduced.

In 3GPP, as DC schemes, DC by an LTE base station and an NR base station connected to EPC, DC by an NR base station connected to 5G core system, and DC by an LTE base station and an NR base station connected to 5G core system are studied (see non-patent documents 12, 16, and 19).

In 3GPP, services (applications may be used) that use direct Link (SL: side Link) communication (also referred to as PC5 communication) are supported in both EPS (Evolved Packet System: evolved packet system) and 5G core systems described later (see non-patent documents 1, 16, 20, 21, 22, and 23). Examples of the service using SL communication include a V2X (Vehicle-to-evaluation) service, a proxy service, and the like.

Prior art literature

Non-patent literature

Non-patent document 1:3GPP TS 36.300V16.2.0

Non-patent document 2:3GPP S1-083461

Non-patent document 3:3GPP TR 36.814V9.2.0

Non-patent document 4:3GPP TR 36.912V16.0.0

Non-patent document 5: "Senarios, requirements and KPIs for 5G mobile and wireless system: scene, requirements and key performance indicators "ICT-317669-METIS/D1.1 for 5G mobile and wireless systems

Non-patent document 6:3GPP TR 23.799V14.0.0

Non-patent document 7:3GPP TR 38.801V14.0.0

Non-patent document 8:3GPP TR 38.802V14.2.0

Non-patent document 9:3GPP TR 38.804V14.0.0

Non-patent document 10:3GPP TR 38.912V16.0.0

Non-patent document 11:3GPP RP-172115

Non-patent document 12:3GPP TS 37.340V16.4.0

Non-patent document 13:3GPP TS 38.211V16.4.0

Non-patent document 14:3GPP TS 38.213V16.4.0

Non-patent document 15:3GPP TS 38.214V16.4.0

Non-patent document 16:3GPP TS 38.300V16.4.0

Non-patent document 17:3GPP TS 38.321V16.3.0

Non-patent document 18:3GPP TS 38.212V16.4.0

Non-patent document 19:3GPP TS 38.331V16.3.1

Non-patent document 20:3GPP TR 23.703V12.0.0

Non-patent document 21:3GPP TS23.501V16.7.0

Non-patent document 22:3GPP TS23.287V16.5.0

Non-patent document 23:3GPP TS23.303V16.0.0

Non-patent document 24:3GPP TS 38.305V16.3.0

Non-patent document 25:3GPP TS23.273V16.5.0

Non-patent document 26:3GPP R2-2009145

Non-patent document 27:3GPP TR 38.836V1.0.1

Disclosure of Invention

Technical problem to be solved by the invention

In addition, a case is studied in which a plurality of services using SL communication (also referred to as PC5 communication) are supported in both the EPS and 5G core systems (see non-patent documents 1, 16, 20, 21, 22, and 23). In SL communication, communication is performed between terminals. In SL communication, communication between a UE and an NW via relay (relay) is proposed as well as direct communication between terminals (see non-patent documents 20, 23, and 27). In such a system supporting communication via relay, how to improve the communication quality between the terminal and NW becomes a problem. For example, in the HO of a remote UE via a relay UE, how to reduce the data communication delay time at the time of HO, how to improve the robustness at the time of HO, and the like.

In view of the above-described problems, it is an object of the present disclosure to improve communication quality in a communication system that utilizes inter-terminal communication.

Technical means for solving the technical problems

The communication system according to the present disclosure includes: a 1 st base station, the 1 st base station being connected to a 1 st communication terminal, the 1 st communication terminal supporting inter-terminal communication in which communication terminals directly communicate with each other; and a 2 nd base station, wherein the 2 nd base station is connected with a 2 nd communication terminal, and the 2 nd communication terminal supports communication between terminals. When a request for switching the 1 st communication terminal to connect to the base station via the 2 nd communication terminal is received, the 2 nd base station transmits communication setting information indicating setting contents for the 1 st communication terminal and the 2 nd communication terminal to perform inter-terminal communication to the 1 st communication terminal and the 2 nd communication terminal.

Effects of the invention

According to the present disclosure, communication quality can be improved in a communication system using inter-terminal communication.

The objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description and accompanying drawings.

Drawings

Fig. 1 is an explanatory diagram showing a configuration of a radio frame used in a communication system of the LTE scheme.

Fig. 2 is a block diagram showing the overall configuration of an LTE communication system 200 discussed in 3 GPP.

Fig. 3 is a block diagram showing the overall structure of the communication system 210 of the NR scheme discussed in 3 GPP.

Fig. 4 is a block diagram of DC based on enbs and gnbs connected to EPC.

Fig. 5 is a block diagram of DC based on a gNB connected to an NG core.

Fig. 6 is a block diagram of DC based on an eNB and a gNB connected to an NG core.

Fig. 7 is a block diagram of DC based on an eNB and a gNB connected to an NG core.

Fig. 8 is a block diagram illustrating the structure of the mobile terminal 202 shown in fig. 2.

Fig. 9 is a block diagram showing the structure of the base station 203 shown in fig. 2.

Fig. 10 is a block diagram showing the structure of an MME.

Fig. 11 is a block diagram showing the structure of the 5GC part.

Fig. 12 is a flowchart showing an outline of a cell search to standby operation performed by a communication terminal (UE) in the LTE communication system.

Fig. 13 is a diagram showing one example of a cell structure in an NR system.

Fig. 14 is a flowchart showing an example of a method of HO of a remote UE via a relay UE in embodiment 1.

Fig. 15 is a flowchart showing another example of a method of HO of a remote UE via a relay UE in embodiment 1.

Fig. 16 is a flowchart showing an example of a method of HO of a remote UE via a relay UE in modification 1 of embodiment 1.

Fig. 17 is a flowchart showing an example of a method of I-DPAS HO in modification 2 of embodiment 1.

Fig. 18 is a flowchart showing another example of the method of I-DPAS HO in modification 2 of embodiment 1.

FIG. 19 is a flowchart showing an example of the method of I-CHO in embodiment 2.

Fig. 20 is a flowchart showing an example of a method of a remote UE performing HO to a HO target gNB of a relay UE in embodiment 3.

Fig. 21 is a flowchart showing another example of a method of the remote UE performing HO to the HO target gNB of the relay UE in embodiment 3.

Fig. 22 is a flowchart showing another example of a method of the remote UE performing HO to the HO target gNB of the relay UE in embodiment 3.

Detailed Description

A communication system and a base station according to an embodiment of the present invention will be described in detail below with reference to the drawings.

Embodiment 1.

Fig. 2 is a block diagram showing the overall structure of a communication system 200 of the LTE scheme discussed in 3 GPP. Fig. 2 is explained. The radio access network is referred to as E-UTRAN (Evolved Universal Terrestrial Radio Access Network: evolved universal terrestrial radio access network) 201. A mobile terminal apparatus (hereinafter referred to as "mobile terminal apparatus") 202, which is a communication terminal apparatus, can perform radio communication with a base station apparatus (hereinafter referred to as "base station (E-UTRAN NodeB) eNB") 203, and transmit and receive signals by radio communication.

Here, the "communication terminal apparatus" includes not only mobile terminal apparatuses such as mobile telephone terminal apparatuses that are mobile but also devices that are not mobile such as sensors. In the following description, the "communication terminal apparatus" may be simply referred to as a "communication terminal".

If a control protocol for the mobile terminal 202, such as RRC (Radio Resource Control: radio resource control), and a user Plane (hereinafter, also referred to as U-Plane) such as PDCP (Packet Data Convergence Protocol: packet data diversity protocol), RLC (Radio Link Control: radio link control), MAC (Medium Access Control: medium access control), PHY (Physical layer) are terminated at the base station 203, the E-UTRNA is composed of one or more base stations 203.

The control protocol RRC (Radio Resource Control) between the mobile terminal 202 and the base station 203 performs Broadcast (Broadcast), paging (paging), RRC connection management (RRC connection management), and the like. The states of the base station 203 and the mobile terminal 202 in RRC are rrc_idle and rrc_connected.

PLMN (Public Land Mobile Network: public land mobile network) selection, broadcast of system information (System Information: SI), paging (paging), cell re-selection (cell re-selection), mobility, etc. are performed at rrc_idle. In rrc_connected, the mobile terminal has an RRC connection (connection) and can transmit and receive data to and from the network. In rrc_connected, handover (HO), measurement (measurement) of Neighbor cells (Neighbor cells), and the like are performed.

The base station 203 is constituted by 1 or more enbs 207. In addition, a system composed of EPC (Evolved Packet Core: evolved packet core) as a core network and E-UTRNA201 as a radio access network is referred to as EPS (Evolved Packet System: evolved packet system). EPC as a core network and E-UTRNA201 as a radio access network are sometimes collectively referred to as "networks".

The eNB207 is connected to a mobility management entity (Mobility Management Entity: MME), an S-GW (Serving Gateway), or an MME/S-GW unit (hereinafter, sometimes referred to as "MME unit") 204 including the MME and the S-GW via an S1 interface, and performs communication of control information between the eNB207 and the MME unit 204. One eNB207 may be connected to a plurality of MME sections 204. The enbs 207 are connected to each other via an X2 interface, and control information is communicated between the enbs 207.

The MME unit 204 is a higher-level device, specifically, a higher-level node, and controls connection between an eNB207 as a base station and a mobile terminal (UE) 202. The MME unit 204 forms an EPC serving as a core network. The base station 203 constitutes E-UTRNA201.

The base station 203 may constitute one cell or may constitute a plurality of cells. Each cell has a predetermined range as a coverage area which is a range capable of communicating with the mobile terminal 202, and performs wireless communication with the mobile terminal 202 within the coverage area. When one base station 203 constitutes a plurality of cells, each cell is configured to be able to communicate with the mobile terminal 202.

Fig. 3 is a block diagram showing the overall structure of the 5G-mode communication system 210 discussed in 3 GPP. Fig. 3 is explained. The radio access network is referred to as NG-RAN (Next Generation Radio Access Network: next generation radio access network) 211. The UE202 can perform radio communication with an NR base station apparatus (hereinafter referred to as "NR base station (NG-RAN NodeB: gNB)") 213, and can perform transmission and reception of signals by radio communication. In addition, the core network is called a 5G core (5G core:5 gc).

The NG-RAN is composed of one or more NR base stations 213 if a control protocol for the UE202, such as RRC (Radio Resource Control: radio resource control), and a user Plane (hereinafter, also sometimes referred to as U-Plane), such as SDAP (Service Data Adaptation Protocol: traffic data adaptation protocol), PDCP (Packet Data Convergence Protocol: packet data diversity protocol), RLC (Radio Link Control: radio link control), MAC (Medium Access Control: medium access control), PHY (Physical layer) is terminated at the NR base station 213.

The function of the control protocol RRC (Radio Resource Control: radio resource control) between the UE202 and the NR base station 213 is the same as LTE. As states between the NR base station 213 and the UE202 in RRC, there are rrc_idle, rrc_connected, and rrc_inactive.

The rrc_idle and rrc_connected are the same as in the LTE scheme. Rrc_inactive performs broadcasting, paging (paging), cell re-selection (cell re-selection), moving, and the like of system information (System Information: SI) while maintaining connection between the 5G core and the NR base station 213.

The gNB217 is connected to an access/mobility management function (Access and Mobility Management Function: AMF), a session management function (Session Management Functio: SMF), or a UPF (User Plane Function: user plane function), or an AMF/SMF/UPF section (hereinafter, referred to as "5GC section") 214 including the AMF, the SMF, and the UPF through a NG interface. Communication of control information and/or user data is performed between the gNB217 and the 5GC part 214. The NG interface is a generic term for an N2 interface between the gNB217 and the AMF, an N3 interface between the gNB217 and the UPF, an N11 interface between the AMF and the SMF, and an N4 interface between the UPF and the SMF. One gNB217 may be connected to a plurality of 5GC portions 214. The gnbs 217 are connected to each other through an Xn interface, and control information and/or user data are communicated between the gnbs 217.

The 5GC unit 214 allocates paging signals to the higher-level devices, specifically, to the higher-level nodes, the one or more base stations 203, and/or the base station 213. The 5GC unit 214 performs mobile Control (Mobility Control) in the standby State (Idle State). The 5GC unit 214 manages a Tracking Area (Tracking Area) list when the mobile terminal 202 is in the standby State and when it is in the Inactive State and the Active State. The 5GC unit 214 starts the paging protocol by transmitting a paging message to a cell belonging to a Tracking Area (Tracking Area) in which the mobile terminal 202 is registered.

NR base station 213 is also identical to base station 203 and may constitute one or more cells. When one NR base station 213 constitutes a plurality of cells, each cell is configured to be able to communicate with the UE 202.

The gNB217 may be divided into a Central Unit (hereinafter, referred to as CU) 218 and a Distributed Unit (hereinafter, referred to as DU) 219.CU218 is formed as one in the gNB 217. The DU219 is configured as one or more in the gNB 217. CU218 is connected to DU219 via an F1 interface, and communication of control information and/or user data is performed between CU218 and DU 219.

The 5G communication system may include a unified data management (Unified Data Management; UDM) function and a policy control function (Policy Control Function; PCF) described in non-patent document 21 (3 gpp ts 23.501). UDM and/or PCF may be included in 5GC portion 214 in fig. 3.

In the 5G communication system, a location management function (Location Management Function:lmf) described in non-patent document 24 (3 gpp ts 38.305) can be provided. As disclosed in non-patent document 25 (3 gpp ts 23.273), the LMF can be connected to the base station via the AMF.

The 5G communication system may include a Non-3GPP interworking function (Non-3GPP Interworking Function:N3IWF) described in Non-patent document 21 (3 GPP ts 23.501). The N3IWF may terminate AN Access Network (AN) with the UE in a non-3GPP Access with the UE.

Fig. 4 is a diagram showing a structure of DC performed by an eNB and a gNB connected to an EPC. In FIG. 4, the solid line represents the connection of U-Plane, and the broken line represents the connection of C-Plane. In fig. 4, eNB223-1 is a primary base station, and gNB224-2 is a secondary base station (this DC structure is sometimes referred to as EN-DC). In fig. 4, an example is shown in which the U-Plane connection between the MME part 204 and the gNB224-2 is performed via the eNB223-1, but may be performed directly between the MME part 204 and the gNB 224-2.

Fig. 5 is a diagram showing a structure of DC based on the gNB connected to the NG core. In FIG. 5, the solid line represents the connection of U-Plane, and the broken line represents the connection of C-Plane. In fig. 5, gNB224-1 is a primary base station and gNB224-2 is a secondary base station (this DC structure is sometimes referred to as NR-DC). In fig. 5, an example is shown in which the U-Plane connection between the 5GC part 214 and the gNB224-2 is made via the gNB224-1, but may be made directly between the 5GC part 214 and the gNB 224-2.

Fig. 6 is a diagram showing a structure of DC based on eNB and gNB connected to NG core. In FIG. 6, the solid line represents the connection of U-Plane, and the broken line represents the connection of C-Plane. In fig. 6, eNB226-1 is a primary base station and gNB224-2 is a secondary base station (this DC structure is sometimes referred to as NG-EN-DC). In fig. 6, an example is shown in which the U-Plane connection between the 5GC part 214 and the gNB224-2 is made via the eNB226-1, but may be made directly between the 5GC part 214 and the gNB 224-2.

Fig. 7 is a diagram showing another structure of DC based on eNB and gNB connected to NG core. In FIG. 7, the solid line represents the connection of U-planes, and the broken line represents the connection of C-planes. In fig. 7, gNB224-1 is a primary base station and eNB226-2 is a secondary base station (this DC structure is sometimes referred to as NE-DC). In fig. 7, an example is shown in which the U-Plane connection between the 5GC part 214 and the eNB226-2 is performed via the gNB224-1, but may be performed directly between the 5GC part 214 and the eNB 226-2.

Fig. 8 is a block diagram illustrating the structure of the mobile terminal 202 shown in fig. 2. The transmission processing of the mobile terminal 202 shown in fig. 8 will be described. First, control data from the protocol processing section 301 and user data from the application section 302 are stored in the transmission data buffer section 303. The data stored in the transmission data buffer 303 is transferred to the encoding unit 304, and encoding processing such as error correction is performed. There may be data directly output from the transmission data buffer unit 303 to the modulation unit 305 without performing the encoding process. The data subjected to the encoding process by the encoding unit 304 is subjected to the modulation process by the modulation unit 305. The modulation unit 305 may perform precoding in MIMO. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 306, and converted into a radio transmission frequency. Thereafter, the transmission signals are transmitted from the antennas 307-1 to 307-4 to the base station 203. In fig. 8, a case where the number of antennas is 4 is illustrated, but the number of antennas is not limited to 4.

Further, the reception process of the mobile terminal 202 is performed as follows. Radio signals from the base station 203 are received through antennas 307-1 to 307-4. The received signal is frequency-converted from radio reception to baseband signal in the frequency conversion unit 306, and is subjected to demodulation processing in the demodulation unit 308. In the demodulation section 308, waiting calculation and multiplication processing can be performed. The demodulated data is transferred to the decoding unit 309, and subjected to decoding processing such as error correction. Of the decoded data, control data is transferred to the protocol processing section 301, and user data is transferred to the application section 302. A series of processes of the mobile terminal 202 is controlled by the control section 310. Thus, although omitted in fig. 8, the control unit 310 is connected to the respective units 301 to 309. The control unit 310 is implemented by a processing circuit including a processor and a memory, for example. That is, the control unit 310 is realized by executing a program describing a series of processes of the mobile terminal 202 by a processor. A program describing a series of processes of the mobile terminal 202 is stored in the memory. Examples of the Memory are nonvolatile or volatile semiconductor memories such as RAM (Random Access Memory: random access Memory), ROM (Read Only Memory), flash Memory, and the like. The control section 310 may be implemented by a dedicated processing circuit such as an FPGA (Field Programmable Gate Array: field programmable gate array), an ASIC (Application Specific Integrated Circuit: application specific integrated circuit), a DSP (Digital Signal Processor: digital signal processor), or the like. In fig. 8, the number of antennas used for transmission by mobile terminal 202 may be the same as or different from the number of antennas used for reception.

Fig. 9 is a block diagram showing the structure of the base station 203 shown in fig. 2. The transmission processing of the base station 203 shown in fig. 9 will be described. The EPC communication unit 401 transmits and receives data between the base station 203 and the EPC (MME unit 204 or the like). The 5GC communication unit 412 transmits and receives data between the base station 203 and the 5GC (5 GC unit 214, etc.). The other base station communication unit 402 performs data transmission and reception with other base stations. The EPC communication unit 401, the 5GC communication unit 412, and the other base station communication unit 402 exchange information with the protocol processing unit 403, respectively. The control data from the protocol processing section 403, and the user data and control data from the EPC communication section 401, the 5GC communication section 412, and the other base station communication section 402 are stored in the transmission data buffer section 404.

The data stored in the transmission data buffer 404 is transferred to the encoding unit 405, and encoding processing such as error correction is performed. There may be data directly output from the transmission data buffer 404 to the modulation unit 406 without performing the encoding process. The coded data is subjected to modulation processing in the modulation section 406. The modulation unit 406 may perform precoding in MIMO. The modulated data is converted into a baseband signal, and then output to the frequency conversion unit 407, where it is converted into a radio transmission frequency. The transmit signals are then transmitted to one or more mobile terminals 202 using antennas 408-1 through 408-4. In fig. 9, a case where the number of antennas is 4 is illustrated, but the number of antennas is not limited to 4.

The reception process of the base station 203 is performed as follows. Wireless signals from one or more mobile terminals 202 are received by antenna 408. The received signal is frequency-converted from radio reception to a baseband signal by the frequency conversion unit 407, and is subjected to demodulation processing by the demodulation unit 409. The demodulated data is transferred to the decoding unit 410, and subjected to decoding processing such as error correction. Among the decoded data, the control data is transmitted to the protocol processing unit 403, the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402, and the user data is transmitted to the 5GC communication unit 412, the EPC communication unit 401, or the other base station communication unit 402. A series of processes of the base station 203 is controlled by the control section 411. Thus, although omitted in fig. 9, the control unit 411 is connected to the respective units 401 to 410, 412. The control unit 411 is implemented by a processing circuit including a processor and a memory, or by a dedicated processing circuit such as FPGA, ASIC, DSP, similarly to the control unit 310 of the mobile terminal 202. In fig. 9, the number of antennas used for transmission by the base station 203 may be the same as or different from the number of antennas used for reception.

Fig. 9 is a block diagram showing the configuration of the base station 203, but the same configuration may be adopted for the base station 213. In addition, with respect to fig. 8 and 9, the number of antennas of the mobile terminal 202 and the number of antennas of the base station 203 may be the same or different.

Fig. 10 is a block diagram showing the structure of an MME. Fig. 10 shows a structure of MME204a included in MME unit 204 shown in fig. 2. The PDN GW communication unit 501 transmits and receives data between the MME204a and the PDN GW (Packet Data Network Gate Way: packet data gateway). The base station communication unit 502 transmits and receives data between the MME204a and the base station 203 via the S1 interface. In the case where the data received from the PDN GW is user data, the user data is transferred from the PDN GW communication section 501 to the base station communication section 502 via the user plane communication section 503 and transmitted to the one or more base stations 203. In the case where the data received from the base station 203 is user data, the user data is transferred from the base station communication section 502 to the PDN GW communication section 501 via the user plane communication section 503, and is transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, the control data is transferred from the PDN GW communication section 501 to the control plane control section 505. When the data received from the base station 203 is control data, the control data is transferred from the base station communication unit 502 to the control plane control unit 505.

The HeNBGW communication unit 504 transmits and receives data between the MME204a and a HeNBGW (Home-eNB gateway). The HeNBGW communication section 504 transfers control data received from the HeNBGW to the control plane control section 505. The HeNBGW communication section 504 transmits the control data input from the control plane control section 505 to the HeNBGW.

The control Plane control unit 505 includes a NAS security unit 505-1, an SAE bearer control unit 505-2, an Idle State (Idle State) mobility management unit 505-3, and the like, and performs all processing for a control Plane (hereinafter, also referred to as C-Plane). The NAS security unit 505-1 performs security and the like of NAS (Non-Access Stratum) messages. The SAE bearer control unit 505-2 manages the SAE (System Architecture Evolution: system architecture evolution) bearer. The Idle State mobility management unit 505-3 performs mobility management in a standby State (Idle State): LTE-Idle State, or simply referred to as Idle State), generation and control of a paging signal in the standby State, addition, deletion, update, search, and tracking area list management of one or more tracking areas of the mobile terminal 202 under coverage.

MME204a allocates paging signals to one or more base stations 203. The MME204a performs Mobility control (Mobility control) in a standby State (Idle State). The MME204a manages a Tracking Area (Tracking Area) list when the mobile terminal 202 is in a standby State and in an Active State (Active State). The MME204a starts a paging protocol by transmitting a paging message to a cell belonging to a Tracking Area (Tracking Area) where the mobile terminal 202 is registered. Management of CSG, management of CSG ID, and whitelist management of eNB207 connected to MME204a may be performed by idle state mobility management unit 505-3.

A series of processes of MME204a is controlled by control unit 506. Thus, although omitted in fig. 10, the control unit 506 is connected to each of the units 501 to 505. The control unit 506 is implemented by a processing circuit including a processor and a memory, or by a dedicated processing circuit such as FPGA, ASIC, DSP, similarly to the control unit 310 of the mobile terminal 202.

Fig. 11 is a block diagram showing the structure of the 5GC part. Fig. 11 shows the structure of the 5GC part 214 shown in fig. 3. Fig. 11 shows a case where the 5GC unit 214 shown in fig. 5 includes the AMF structure, the SMF structure, and the UPF structure. The Data Network (Data Network) communication unit 521 transmits and receives Data between the 5GC unit 214 and the Data Network. The base station communication unit 522 transmits and receives data via the S1 interface between the 5GC unit 214 and the base station 203, and/or transmits and receives data via the NG interface between the 5GC unit 214 and the base station 213. In the case where the data received from the data network is user data, the user data is transferred from the data network communication unit 521 to the base station communication unit 522 via the user plane communication unit 523, and is transmitted to one or more base stations 203 and/or 213. When the data received from the base station 203 and/or the base station 213 is user data, the user data is transmitted from the base station communication unit 522 to the data network communication unit 521 via the user plane communication unit 523, and is transmitted to the data network.

When the data received from the data network is control data, the control data is transmitted from the data network communication unit 521 to the session management unit 527 via the user plane communication unit 523. The session management section 527 transfers the control data to the control plane control section 525. When the data received from the base station 203 and/or the base station 213 is control data, the control data is transmitted from the base station communication unit 522 to the control plane control unit 525. The control plane control unit 525 transfers the control data to the session management unit 527.

The control Plane control unit 525 includes a NAS security unit 525-1, a PDU session control unit 525-2, an Idle State (Idle State) mobility management unit 525-3, and the like, and performs all processing for a control Plane (hereinafter, also referred to as C-Plane). The NAS security unit 525-1 performs security and the like of NAS (Non-Access Stratum) messages. The PDU session control unit 525-2 manages the PDU session between the mobile terminal 202 and the 5GC unit 214, and the like. The Idle State mobility management unit 525-3 performs mobility management in a standby State (Idle State): rrc_idle State, or simply referred to as Idle), generation and control of a paging signal in the standby State, addition, deletion, update, search, and tracking area list management of one or more tracking areas of the mobile terminal 202 under coverage.

The series of processes of the 5GC part 214 is controlled by the control part 526. Accordingly, although omitted in fig. 11, the control section 526 is connected to the respective sections 521 to 523, 525, 527. The control unit 526 is implemented by a processing circuit including a processor and a memory, or by a dedicated processing circuit such as FPGA, ASIC, DSP, similarly to the control unit 310 of the mobile terminal 202.

Next, one example of a cell search method in a communication system is shown. Fig. 12 is a flowchart showing an outline of a communication terminal (UE) from cell search to standby operation in the LTE communication system. When the communication terminal starts cell search, in step ST601, the communication terminal acquires synchronization of slot timing and frame timing by using the first synchronization signal (P-SS) and the second synchronization signal (S-SS) transmitted from the peripheral base station.

The P-SS and S-SS are collectively referred to as a synchronization signal (Synchronization Signal: SS). A synchronization code corresponding to the PCI assigned to each cell is assigned to the Synchronization Signal (SS). The number of PCIs was investigated to be 504. The communication terminal acquires synchronization using the 504 PCIs, and detects (determines) PCIs of cells that acquired synchronization.

Next, in step ST602, the communication terminal detects a Cell-specific reference signal (Cell-specific Reference Signal: CRS), which is a reference signal (reference signal: RS) transmitted from the base station to each Cell, for the synchronized cells, and measures the received power (Reference Signal Received Power: RSRP) of the RS. The Reference Signal (RS) uses codes that are one-to-one corresponding to the PCIs. The code can be used to derive a correlation to separate from other cells. By deriving the RS code of the cell from the PCI determined in step ST601, the RS can be detected and the received power of the RS can be measured.

Next, in step ST603, the communication terminal selects a cell having the best reception quality of the RS, for example, a cell having the highest reception power of the RS, that is, the best cell, from among the one or more cells detected up to step ST 602.

Next, in step ST604, the communication terminal receives the PBCH of the best cell and obtains broadcast information, that is, BCCH. The BCCH on the PBCH is mapped with MIB (Master Information Block: master information block) containing cell structure information. Thus, MIB can be obtained by receiving PBCH and obtaining BCCH. As the information of MIB, there are, for example, DL (downlink) system bandwidth (also referred to as transmission bandwidth setting (transmission bandwidth configuration: DL-bandwidth)), the number of transmission antennas, SFN (System Frame Number: system frame number), and the like.

Next, in step ST605, the communication terminal receives the DL-SCH of the cell based on the cell structure information of the MIB and obtains SIB (System Information Block: system information block) 1 in the broadcast information BCCH. The SIB1 contains information related to access to the cell, information related to cell selection, and scheduling information of other SIBs (SIBk; integer k.gtoreq.2). The SIB1 also contains a tracking area code (Tracking Area Code: TAC).

Next, in step ST606, the communication terminal compares the TAC of SIB1 received in step ST605 with the TAC part of the tracking area identification (Tracking Area Identity: TAI) in the tracking area list held by the communication terminal. The tracking area list is also called a TAI list (TAI list). The TAI is identification information for identifying the tracking area, and is composed of MCC (Mobile Country Code: mobile country code), MNC (Mobile Network Code: mobile network code), and TAC (Tracking Area Code: tracking area code). MCC is a country code. MNC is a network code. The TAC is the code number of the tracking area.

If the TAC received in step ST605 is the same as the TAC included in the tracking area list as a result of the comparison in step S606, the communication terminal enters a standby operation in the cell. If the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a change of tracking area to the Core Network (EPC) including the MME or the like through the cell, and performs TAU (Tracking Area Update: tracking area update).

In the example shown in fig. 12, an example of the operation from cell search to standby in the LTE scheme is shown, but in the NR scheme, the best beam may be selected in addition to the best cell in step ST 603. In the NR scheme, in step ST604, beam information, for example, beam identification, may be acquired. In the NR scheme, in step ST604, scheduling information of the remaining minimum SI (Remaining Minimum SI (remaining minimum system information): RMSI) may be acquired. In the NR system, in step ST605, RMSI may be received.

A device constituting the core network (hereinafter, sometimes referred to as a "core network side device") updates the tracking area list based on the TAU request signal and the identification number (UE-ID or the like) of the communication terminal transmitted from the communication terminal. And the core network side device sends the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) the TAC list held by the communication terminal based on the received tracking area list. Thereafter, the communication terminal enters a standby operation in the cell.

Due to the popularity of smartphones and tablet terminal devices, traffic volume by wireless communication using a cellular system has exploded, and there is a concern about shortage of wireless resources worldwide. In order to cope with this situation, the miniaturization of cells and the advance of space separation have been studied to improve the frequency utilization efficiency.

In the existing cell structure, a cell composed of enbs has a wide coverage range. Conventionally, a cell is configured so as to cover a certain area by a wide coverage of a plurality of cells configured by a plurality of enbs.

When the cell is miniaturized, the cell constituted by the eNB has a coverage area narrower than that of the cell constituted by the conventional eNB. Therefore, in order to cover a certain area, a large number of enbs with small cells are required as compared with the conventional enbs, as in the prior art.

In the following description, as in a cell configured by a conventional eNB, a cell having a relatively large coverage area is referred to as a "macro cell", and an eNB configuring the macro cell is referred to as a "macro eNB". In addition, as a cell in which the cell is miniaturized, a cell having a relatively small coverage area is referred to as a "small cell", and an eNB constituting the small cell is referred to as a "small eNB".

The macro eNB may be, for example, "wide area base station (Wide Area Base Station)" described in non-patent document 7.

Small enbs may be, for example, low power nodes, local nodes, hotspots, etc. Further, the small eNB may be a pico eNB constituting a pico cell (pico cell), a femto eNB, heNB, RRH constituting a femto cell (femto cell) (Remote Radio Head: remote radio head), an RRU (Remote Radio Unit: remote radio unit), an RRE (Remote Radio Equipment: remote radio device) or an RN (Relay Node). The small eNB may be a "local base station (Local Area Base Station)" or a "home base station (Home Base Station)" described in non-patent document 7.

Fig. 13 shows one example of the structure of cells in NR. In the NR cell, a narrower beam is formed and changed in direction to transmit. In the example shown in fig. 13, the base station 750 uses the beam 751-1 to transmit and receive with a mobile terminal at a certain time. At other times, the base station 750 uses the beam 751-2 for transceiving with the mobile terminal. The base station 750 uses one or more of the beams 751-3 to 751-8 to transmit and receive with the mobile terminal in the same manner as described below. Thus, the base station 750 constitutes a wide range of cells.

In fig. 13, an example is shown in which the number of beams used by the base station 750 is set to 8, but the number of beams may be different from 8. In the example shown in fig. 13, the number of beams used by the base station 750 at the same time is set to one, but may be plural.

In 3GPP, D2D (Device to Device) communication and V2V (Vehicle to Vehicle: car) communication support a through Link (SL: side Link) (see non-patent document 1 and non-patent document 16). SL is specified by the PC5 interface.

A physical channel for SL (see non-patent document 1) is described. The physical through link broadcast channel (PSBCH: physical sidelink broadcast channel) transmits information related to system synchronization and is transmitted from the UE.

A physical through link discovery channel (PSDCH: physical sidelink discovery channel) transmits through link discovery messages from UEs.

A physical through link control channel (PSCCH: physical sidelink control channel) conveys control information from UEs for through link communications with V2X through links.

A physical through link shared channel (PSSCH: physical sidelink shared channel) transmits data from the UE for through link communication with the V2X through link communication.

A physical through link feedback channel (PSFCH: physical sidelink feedback channel) transmits HARQ feedback on the through link from a UE receiving a PSSCH transmission to a UE transmitting the PSSCH.

A transmission channel for SL (see non-patent document 1) is described. The through link broadcast channel (SL-BCH: sidelink broadcast channel) has a predetermined transport channel format and is mapped to PSBCH, which is a physical channel.

The direct link discovery channel (SL-DCH: sidelink discovery channel) has a fixed size periodic broadcast transmission in a predetermined format. In addition, the SL-DCH supports both UE automatic resource selection (UE autonomous resource selection) and resource allocation scheduled by the eNB. There is a risk of collision in the UE's automatic resource selection, and there is no collision when the UE allocates dedicated resources through the eNB. Furthermore, the SL-DCH supports HARQ combining, but does not support HARQ feedback. The SL-DCH is mapped to a PSDCH as a physical channel.

The direct link shared channel (SL-SCH: sidelink shared channel) supports broadcast transmissions. The SL-SCH supports both UE automatic resource selection (UE autonomous resource selection) and resource allocation scheduled by the eNB. There is a risk of collision in the UE's automatic resource selection, and there is no collision when the UE allocates dedicated resources through the eNB. In addition, SL-SCH supports HARQ combining but does not support HARQ feedback. In addition, the SL-SCH supports dynamic link adaptation by varying transmit power, modulation, combining. The SL-SCH is mapped to the PSSCH which is the physical channel.

A logical channel for SL (see non-patent document 1) is described. The through link broadcast control channel (SBCCH: sidelink Broadcast Control Channel) is a through link channel for broadcasting through link system information from one UE to other UEs. The SBCH is mapped to SL-BCH as a transmission channel.

The direct link traffic channel (STCH: sidelink Traffic Channel) is a one-to-many direct link traffic channel for transmitting user information from one UE to other UEs. STCH is used only by UEs with through link communication capability and UEs with V2X through link communication capability. One-to-one communication between two through link communication capable UEs is also additionally achieved through the STCH. The STCH is mapped to the SL-SCH as a transport channel.

The through link control channel (SCCH; sidelink Control Channel) is a through link control channel for transmitting control information from one UE to another UE. The SCCH is mapped to the SL-SCH as a transport channel.

In 3GPP, V2X communication is also being discussed in NR. The V2X communication in NR is being studied based on the LTE system and the LTE-a system, but in the following, changes and additions from the LTE system and the LTE-a system are performed.

In LTE, SL communication is broadcast only (broadcast). In NR, support of unicast (unicast) and multicast (groupcast) has been studied as SL communication (see non-patent document 22 (3 gpp ts 23.287)).

In unicast communication and multicast communication, support of HARQ feedback (Ack/Nack), CSI reporting, and the like is studied.

In SL communication, in addition to broadcasting, support of PC5-S signaling is studied in order to support unicast (unicast) and multicast (groupcast) (see non-patent document 22 (3 gpp ts 23.287)). For example, PC5-S signaling is implemented in order to establish a SL, i.e. a link for implementing PC5 communications. This link is implemented in the V2X layer, also known as a layer 2 link.

In addition, in SL communication, support of RRC signaling is being studied (see non-patent document 22 (3 gpp ts 23.287)). RRC signaling in SL communication is also referred to as PC5 RRC signaling. For example, there are proposed a capability of notifying UEs between UEs performing PC5 communication, a setting of an AS layer for performing V2X communication using PC5 communication, and the like.

In SL communication, communication between a UE and an NW via relay (relay) is proposed (see non-patent document 20 (3 gpp tr 23.703), non-patent document 23 (3 gpp ts 23.303), and non-patent document 27 (3 gpp tr 38.836)). The relay between the UE and NW is sometimes referred to as a UE-to-NW relay or an inter-UE-NW relay. In the present disclosure, a UE that performs relay between the UE and NW is sometimes referred to as a relay UE.

For example, not only UEs within coverage of a RAN node (e.g., a gNB), but also UEs that are farther away are sometimes required to communicate with the RAN node. In this case, a method using inter-UE-NW relay is considered. For example, communication between the gNB and a UE (sometimes referred to as a remote UE) is conducted via a relay UE. Communication between the gNB and the relay UE is performed by Uu, and communication between the relay UE and the remote UE is performed by PC 5.

For example, both relay UEs and remote UEs are sometimes located within the coverage of the gNB. The gcb in which the relay UE is present in the coverage (hereinafter, sometimes referred to as gcb#1) may be the same as or different from the gcb in which the remote UE is present in the coverage (hereinafter, sometimes referred to as gcb#2). In this case, it is also possible to consider that the remote UE communicates with the gcb where the relay UE exists via the relay UE.

For example, when a remote UE connected to the gnb#2 exists at the coverage end of the gnb#2, good communication quality may not be obtained. In this case, the remote UE can obtain better communication quality by connecting to the gnb#1 via the relay UE. Further, for example, when the radio propagation loss between the remote UE and the relay UE is smaller than the radio propagation loss between the remote UE and the gnb#2, the remote UE can communicate with the gnb#1 via the relay UE, and thus the transmission power of the remote UE can be reduced, and thus the power consumption can be reduced.

In 3GPP, a method of performing HO (HandOver: handOver) from a directly connected gNB to an indirectly connected gNB via a relay UE by a remote UE is studied (see non-patent document 26 (3 GPP R2-2009145)). However, in HO of a remote UE to an indirectly connected gNB via a UE, SL communication (hereinafter sometimes referred to as PC5 communication) between the remote UE and a relay UE is required unlike HO between conventional gnbs to which the remote UE is directly connected.

In PC5 communication, a transmitting side UE (hereinafter, sometimes referred to as UE-TX) sets a receiving side UE (hereinafter, sometimes referred to as UE-RX) for communication in a direction from UE-TX to UE-RX. As a setting for communication from UE-TX to UE-RX, there is, for example, RRC setting or the like (see non-patent document 19 (3 gpp ts 38.331)). However, no detailed setting method for PC5 communication in HO of a remote UE to an indirectly connected gNB via a relay UE or HO of a remote UE from an indirectly connected gNB via a relay UE, in other words, HO of a remote UE via a relay UE is disclosed in non-patent literature 19, other literature, and the like. Therefore, only the conventional method is applied, and there is a problem in that HO of a remote UE via a relay UE cannot be performed.

In embodiment 1, a method for solving such a problem is disclosed. In the following description, settings for PC5 communication are sometimes referred to as settings necessary for PC5 communication, settings for PC5 communication, and the like.

In order to solve the above-described problem, in the communication system according to the present embodiment, the HO target gNB (hereinafter, sometimes referred to as T-gNB) notifies the remote UE of settings necessary for PC5 communication between the remote UE and the relay UE. Further, the T-gNB notifies the relay UE of settings required for PC5 communication between the remote UE and the relay UE. The relay UE is a relay UE connected or connectable to the T-gNB via which the remote UE is connected to the T-gNB. In the present specification, this relay UE, in other words, the connection target relay UE is sometimes referred to as relay ue#2. In addition, the gNB to which the remote UE performing HO is connected before starting HO is sometimes referred to as a HO-source gNB or S-gNB.

The T-gNB notifies the remote UE and the relay ue#2 of settings used in PC5 communication from the remote UE to the relay ue#2. A notification method of settings used in PC5 communication from a remote UE to a relay UE is disclosed.

The T-gNB notifies the remote UE of settings used in PC5 communication from the remote UE to relay UE #2. The T-gNB may notify the remote UE of the setting via the S-gNB. In the case where the S-gNB is connected to the remote UE via the relay UE, the remote UE may be notified of the setting via the T-gNB, S-gNB, and relay UE. In the present specification, the relay UE when the remote UE is connected to the S-gNB via the relay UE, in other words, the connection source relay UE which is the relay UE connected before the remote UE starts HO is sometimes referred to as a relay UE #1. The T-gNB and S-gNB may be the same gNB. This may be the case for HO between different cells of the same gNB.

As this setting notified to the remote UE, a setting concerning only Transmission (TX) in the PC5 communication from the remote UE to the relay UE #2 may be notified. As the setting notified to the remote UE, settings related to both Transmission (TX) and Reception (RX) in the PC5 communication from the remote UE to the relay UE #2 may be notified. These settings may be notified in combination.

The remote UE notifies the relay ue#2 of a setting used for PC5 communication from the remote UE to the relay ue#2. That is, the remote UE notifies the setting received from the T-gNB. The remote UE may notify the settings received via the S-gNB. The remote UE may notify some or all of the parameters set in the remote UE. As this setting notified from the remote UE to the relay ue#2, settings related to both TX and RX in PC5 communication from the remote UE to the relay ue#2 may be notified. As this setting notified from the remote UE to the relay ue#2, a setting related to TX only in PC5 communication from the remote UE to the relay ue#2 may not be notified.

The notification from the T-gNB to the S-gNB may use an inter-base station interface. The notification may use Xn signaling. For example, it may be notified in a response message to the HO request. Thus, xn signaling can be not additionally notified, and thus reduction in the amount of signaling is achieved. The notification from the S-gNB to the remote UE may use RRC signaling. For example, it may be included in the RRCreconfiguration message to notify. Thus, RRC signaling is not required to be separately notified, and thus the amount of signaling can be reduced. In the case where the remote UE is connected to the S-gNB via the relay UE #1, the notification from the S-gNB to the remote UE may be made via the relay UE # 1.

The relay UE #2 may be notified from the remote UE using PC5-S signaling. May be included in a direct communication request (Direct Communication Request) message. May be included in the security protection PC5-S message for notification. As another method, RRC signaling of SL may be used for notification from the remote UE to the relay UE # 2. May be included in a PC5-RRC message for notification. May be included in the rrcreconfigurable sip message. As other methods, notification may be included in an RRC message notified to the T-gNB from the remote UE. May be included in the rrcreconfigured notification complete message. Relay UE #2 may receive the message notified to the T-gNB from the remote UE to acquire the setting.

Regarding settings used in PC5 communication, 8 examples are disclosed below.

(1) Settings used in the establishment of the PC5-S link.

(2) Settings used in PC5-RRC signaling.

(3) Settings used in PC5-S signaling.

(4) Setting related to SLRB (Side Link Radio Bearer: through link radio bearer).

(5) Setting related to mapping of SLRB and Uu RB.

(6) Setting related to CH of SL.

(7) Information about UEs that are targets for PC5 communication.

(8) Combinations of (1) to (7).

As the setting related to SLRB of (4), 3 examples are disclosed below.

(4-1) setting related to SL SRB (Signaling Radio Bearer: signaling radio bearer).

(4-2) setting related to SL DRB (Data Radio Bearer: data radio bearer).

(4-3) a combination of (4-1) and (4-2).

As the setting related to SL SRB of (4-1), 5 examples are disclosed below.

(4-1-1) settings related to SL SRB 0.

(4-1-2) settings related to SL SRB 1.

(4-1-3) settings related to SL SRB 2.

(4-1-4) settings related to SL SRB 3.

(4-1-5) (4-1-1) to (4-1-4).

The DC using the relay UE may be set. For example, when setting DC using the relay UE, (4-1-4) setting concerning SL SRB3 may be performed.

As the SL DRB, a default DRB, which is set in advance, may be set. The SL DRB-related setting of (4-2) may be a default DRB-related setting. The setting related to the SL DRB may be a setting of whether to use a default DRB. This enables setting of SL DRBs suitable for service later. Further, a default DRB may be used before setting a SL DRB suitable for service. The setting of the SL DRB can be flexibly performed.

The setting related to the mapping of the SLRB and Uu RB in (5) may be a setting related to the mapping of the SLRB used between the remote UE and the relay UE and the Uu RB used between the relay UE and the gNB in the communication between the remote UE and the gNB.

As the setting related to CH of SL of (6), 3 examples are disclosed below.

(6-1) setting related to the SCCH.

(6-2) STCH-related settings.

(6-3) a combination of (6-1) and (6-2).

(7) The information on the UE to be the PC5 communication target may be, for example, information on the transmission target UE for PC5 communication. May be information about the transmission source UE communicating with the PC 5. As the information about the UE, for example, a UE identity may be mentioned. The UE identity may be, for example, an L2ID. The information on the transmission target UE in communication with the PC5 may be, for example, a destination L2ID. The information on the transmission source UE communicating with the PC5 may be, for example, a transmission source L2ID.

Thus, the remote UE can acquire, from the T-gNB, a setting to be used for PC5 communication from the remote UE to the relay UE # 2. Relay ue#2 can acquire settings used in PC5 communication from a remote UE to relay ue#2 from T-gNB.

Other notification methods of settings used in PC5 communications from a remote UE to a relay UE are disclosed. The T-gNB notifies the remote UE of settings used in PC5 communication from the remote UE to relay UE # 2. The method can be suitably applied to the method disclosed above. The remote UE can obtain settings from the T-gNB for use in PC5 communications between the remote UE and relay UE # 2.

The T-gNB may notify the relay ue#2 of settings used in PC5 communication from the remote UE to the relay ue#2. The T-gNB may inform some or all of the parameters set in the remote UE. As this setting notified from the T-gNB to the relay ue#2, settings related to both TX and RX in PC5 communication from the remote UE to the relay ue#2 may be notified. As this setting notified from the T-gNB to the relay ue#2, a setting concerning only TX in PC5 communication from the remote UE to the relay ue#2 may not be notified. The notification from the T-gNB to the relay ue#2 may be performed using a Uu interface between the T-gNB and the relay ue#2. The notification may be performed using RRC signaling. For example, it may be included in the RRCreconfiguration message to notify. For example, the notification may be included in a message requesting a relay between the remote UE and the gNB. Alternatively, the RRC message may be newly set for notification of the setting.

Thus, the relay ue#2 can acquire settings used for PC5 communication from the remote UE to the relay ue#2 from the T-gNB. In addition, since notification from the remote UE to the relay ue#2 is not necessary, the setting can be advanced. Further, since there is no need to perform communication between the remote UE and the relay UE #2 for this setting, SRB0 of SL between the remote UE and the relay UE #2 can be set.

The T-gNB notifies the remote UE and the relay ue#2 of settings used in PC5 communication from the relay ue#2 to the remote UE. A notification method of settings used in PC5 communication from relay UE#2 to a remote UE is disclosed.

The T-gNB notifies the remote UE of settings used in PC5 communication from the relay UE #2 to the remote UE. The notification method can be appropriately applied to the notification method of the setting used in the PC5 communication from the remote UE to the relay UE #2 disclosed above. As this setting notified to the remote UE, settings related to both TX and RX in PC5 communication from relay UE #2 to the remote UE may be notified. As this setting notified to the remote UE, a setting related to only TX in PC5 communication from relay UE #2 to the remote UE may be notified. These settings may be notified in combination.

The remote UE may notify the relay UE #2 of a setting used in PC5 communication from the relay UE #2 to the remote UE. In this case, the remote UE notifies the setting received from the T-gNB. The remote UE may notify the settings received via the S-gNB. As this setting notified from the remote UE to the relay UE #2, settings related to both TX and RX in PC5 communication from the relay UE #2 to the remote UE may be notified. As this setting notified from the remote UE to the relay UE #2, a setting concerning only TX in PC5 communication from the relay UE #2 to the remote UE may be notified. These settings may be notified in combination. The notification method can be appropriately applied to the notification method of the setting used in the PC5 communication from the remote UE to the relay UE #2 disclosed above.

Thus, the remote UE can acquire, from the T-gNB, a setting to be used for PC5 communication from the relay ue#2 to the remote UE. Relay ue#2 can acquire settings used in PC5 communication from relay ue#2 to a remote UE from T-gNB.

Other notification methods of settings used in PC5 communication from relay UE #2 to remote UE are disclosed. The notification method from the T-gNB to the remote UE may be appropriately applied to the notification method of the settings used in the PC5 communication from the remote UE to the relay UE #2 disclosed above. As the setting to be notified to the remote UE, a part or all of parameters set from the T-gNB to the relay UE #2, which will be described later, may be notified. As this setting notified to the remote UE, settings related to both TX and RX in PC5 communication from relay UE #2 to the remote UE may be notified. As this setting notified to the remote UE, a setting concerning only transmission TX in the PC5 communication from the relay UE #2 to the remote UE may not be notified. Thus, the remote UE can acquire, from the T-gNB, a setting to be used for PC5 communication from the relay ue#2 to the remote UE.

The T-gNB notifies the relay ue#2 of a setting used for PC5 communication from the relay ue#2 to the remote UE. As the setting notified from the T-gNB to the relay ue#2, settings related to both TX and RX in PC5 communication from the relay ue#2 to the remote UE may be notified. As this setting notified from the T-gNB to the relay ue#2, a setting concerning only TX in PC5 communication from the relay ue#2 to the remote UE may be notified. These settings may be notified in combination. The notification method from the T-gNB to the relay ue#2 can be appropriately applied to the notification method of the setting necessary for the PC5 communication from the remote UE to the relay ue#2 disclosed above.

Thus, the relay ue#2 can acquire, from the T-gNB, a setting used for PC5 communication from the relay ue#2 to the remote UE. Further, since notification from the relay ue#2 to the remote UE is not required, the setting can be advanced. In addition, since there is no need to perform communication between the relay ue#2 and the remote UE for this setting, SRB0 of SL between the relay ue#2 and the remote UE can be set.

Other notification methods of settings from T-gNB to remote UE for use in PC5 communications from relay UE #2 to remote UE are disclosed. The T-gNB notifies the relay ue#2 of a setting used for PC5 communication from the relay ue#2 to the remote UE. The notification method can be appropriately applied to the notification method disclosed above. The relay UE #2 notifies the remote UE of settings used for PC5 communication from the relay UE #2 to the remote UE. Relay UE #2 notifies the setting received from T-gNB. As this setting notified from relay ue#2 to the remote UE, settings related to both TX and RX in PC5 communication from relay ue#2 to the remote UE may be notified. As this setting notified from the remote UE to the relay ue#2, not only the setting concerning TX in the PC5 communication from the relay ue#2 to the remote UE may be notified.

The remote UE from relay UE #2 may be notified using PC5-S signaling. May be included in a direct communication request (Direct Communication Request) message. May be included in the security protection PC5-S message for notification. As another method, RRC signaling of SL may be used to notify from relay ue#2 to remote UE. May be included in a PC5-RRC message for notification. May be included in the rrcreconfigurable sip message. As another method, the notification may be included in an RRC message that the T-gNB notifies the remote UE via relay ue#2. May be included in the RRCreconfiguration message.

Thus, the remote UE can acquire, from the T-gNB, a setting to be used for PC5 communication from the relay ue#2 to the remote UE.

The notification method of the settings used in the PC5 communication from the remote UE to the relay UE #2 and the notification method of the settings used in the PC5 communication from the relay UE #2 to the remote UE may be used in appropriate combination. This can notify the setting used for the bidirectional PC5 communication between the remote UE and the relay UE # 2. The remote UE and the relay UE #2 can acquire settings used in the bidirectional PC5 communication between the remote UE and the relay UE #2, respectively.

Fig. 14 is a flowchart showing an example of a method of HO of a remote UE via a relay UE in embodiment 1. In step ST1401, the remote UE performs data communication between the S-gNB and the CN. As CN, for example, UPF is available. In step ST1402, the S-gNB notifies the remote UE of the setting of the measurement. As the measurement setting, DL measurement setting and SL measurement setting may be combined. The gNB and the UE may be combined as a measurement object. The measurement setting for gNB is DL and the measurement setting for UE is SL. In DL measurement and SL measurement settings, different frequencies may be set, or the same frequency may be set. DL measurements and SL measurements may be made in the set frequencies. The remote UE performs the measurements in accordance with the measurement settings received from the S-gNB.

In step ST1403, the remote UE performs discovery processing to detect the relay UE. The remote UE detects a relay UE connectable to the gNB through a discovery process. The discovery process may be performed for a UE to be reported in measurement settings. The discovery process may be performed before the SL measurement, and the SL measurement may be performed for the relay UE detected in the discovery process.

The relay UE may notify the remote UE of information about the relay UE, information of the gcb of the connection target of the relay UE, status information of the relay UE, information indicating whether the relay UE can relay, and the like. As the information about the relay UE, an identity of the relay UE may be used. As the information of the gcb of the connection target of the relay UE, the identification of the gcb may be used. The state information of the relay UE may be RRC connection state with the gNB or CM (Connection Management: connection management) connection state with the CN. As information indicating whether or not the relay UE can relay, information on the service may be included. The information on the service may be, for example, information indicating a service that can be relayed.

The relay UE may notify the remote UE of this information in the discovery process. The relay UE may inform the remote UE of this information through PC5-S signaling. Alternatively, the relay UE may notify the remote UE of this information through PC5-RRC signaling. The PC5 connection establishment processing is effective when the PC5 connection is established between the remote UE and the relay UE, for example, when the PC5 connection establishment processing is performed following the discovery processing. As other methods, the relay UE may broadcast the information. The remote UE may receive the information broadcast from the relay UE. Thus, the remote UE can acquire this information.

In step ST1404, the remote UE reports the measurement result to the S-gNB. The DL measurement and the SL measurement may be reported in combination. Reporting of measurement results of SL may be performed for relay UEs detected in the discovery process. DL measurement results and SL measurement results are included in the measurement report message. The SL measurement result may include information on the target relay UE, information on the gcb to which the relay UE is connected, status information of the relay UE, information indicating whether the relay UE can relay, and the like. Thus, the S-gNB can acquire the measurement result of the relay UE in the remote UE.

In step ST1405, the S-gNB decides on HO of the remote UE. The S-gNB may determine a HO of the remote UE using a measurement result, information about the relay UE, information of the gNB to which the relay UE is connected, status information of the relay UE, information indicating whether the relay UE can relay, and the like. Here, it is decided to change the connection destination of the remote UE from S-gNB to relay UE. The S-gNB decides to set the T-gNB connected to the relay UE as the HO target.

In step ST1406, the S-gNB notifies the T-gNB of the HO request of the remote UE. The HO request message may include information about the remote UE, such as an identity of the remote UE, a context of the remote UE, and the like. The HO request message may include information on the relay UE to be a connection target, for example, an identification of the relay UE, information indicating whether the relay UE can relay, and the like. Thus, the T-gNB can acquire information on the remote UE to be HO and the relay UE to be the connection target.

T-gNB receiving information on a remote UE to be HO target and a relay UE to be connection target from S-gNB performs HO reception control on the remote UE. In the HO reception control, the T-gNB judges whether or not HO reception can be performed via relay to the remote UE connection, and performs RRC setting of the remote UE in the T-gNB. The T-gNB can set a PC5 communication between the remote UE and the relay UE. As the PC5 communication setting, RRC setting can be performed. Thus, the T-gNB can notify the PC5 of the communication setting to the remote UE and the relay UE.

The PC5 communication setting between the remote UE and the relay UE may be performed after receiving a relay response from the relay UE, which will be described later. In the case where the relay UE notifies the setting, the following method may be adopted: the T-gNB notifies via the S-gNB and the remote UE; or the T-gNB notifies the relay UE of the HO request message or the like directly from the T-gNB. Thus, the T-gNB can set the PC5 communication using the relay response from the relay UE.

In step ST1407, the T-gNB notifies the relay UE that is the connection target of the remote UE to be HO of the relay request message. The relay request message may include information about the remote UE. The relay request message may include information about the relay UE. Information indicating whether the relay UE can relay may be included. May contain information related to the service. The relay request message may include information indicating the content of the PC5 communication setting set by the T-gNB (hereinafter, referred to as PC5 communication setting information). The PC5 communication setting information is one example of communication setting information indicating setting contents of PC5 communication, which is inter-terminal communication between the remote UE and the relay UE. In the example of fig. 14, the T-gNB includes setting information for PC5 communication from the relay UE to the remote UE in a relay request message, and notifies the relay UE of the setting information. The relay UE that received the notification performs connection acceptance control of the remote UE that is the target of HO. In connection acceptance control of the remote UE, the relay UE determines whether or not it can connect to the remote UE. That is, the relay UE determines whether or not it can connect to the remote UE and relay. In step ST1408, the relay UE notifies the T-gNB of the relay response message. The relay response message may include information on the remote UE, information on the relay UE, and information indicating whether the relay UE can relay the remote UE to be HO. The relay response message may include information indicating that the PC5 has completed the communication setting. In the example of fig. 14, as the relay response message, a positive response is notified.

In step ST1407, the T-gNB notifies the relay UE that is the connection destination of the remote UE to be HO of information on the setting of the adaptation layer. The T-gNB may include this information in the relay request message for notification. The above disclosed method for notifying the setting information for PC5 communication of the relay UE to be the connection destination of the remote UE to be HO from the T-gNB can be suitably applied. As information on the setting of the adaptation layer, information on the setting of the adaptation layer between the remote UE and the relay UE and/or information on the setting of the adaptation layer between the relay UE and the T-gNB, which is used in communication between the remote UE and the T-gNB, may be set. The relay UE that receives the information on the setting of the adaptation layer can perform the setting of the adaptation layer. The relay UE may include information indicating that the setting of the adaptation layer is completed in the relay response message transmitted in step 1408. Thus, the T-gNB can recognize that the setting of the adaptation layer is completed for the relay UE.

In step ST1409, the T-gNB notifies the S-gNB of the HO request response message. In the example of fig. 14, a positive response is notified as a HO request response message. The HO request response message may include information about the remote UE. The HO request response message may include information about the relay UE. Information indicating whether the relay UE can relay may be included. The HO request response message may include RRC settings for communication with the T-gNB, which are set by the T-gNB for the remote UE. The HO request response message may include PC5 communication setting information set by the T-gcb. In the example of fig. 14, the T-gNB includes setting information for PC5 communication from the remote UE to the relay UE in the HO request response message, and notifies the S-gNB.

In step ST1409, the T-gNB may notify the S-gNB of information about the settings of the adaptation layer used in the communication between the remote UE and the T-gNB. This information may be included in the HO request response message to inform. In this notification, the above-disclosed method of notifying the PC5 communication setting information from the T-gNB to the S-gNB can be suitably applied. As the information on the setting of the adaptation layer, information on the setting of the adaptation layer between the remote UE and the relay UE and/or information on the setting of the adaptation layer between the relay UE and the T-gNB used in communication between the remote UE and the T-gNB may be notified.

In step ST1410, the S-gcb notifies the remote UE to be HO of an RRC message for changing the RRC setting (may be an HO instruction) to the T-gcb. The S-gNB may notify the message via the relay UE. As the RRC message, an rrcrecon configuration message may be used. The RRC message may include information about the remote UE. The RRC message may include information about the relay UE that is the connection target. The RRC message may include information on the T-gNB that is the HO target. The RRC message may include an RRC setting for communication between the remote UE set by the T-gNB and the T-gNB. Thus, the remote UE can receive the RRC setting set by the T-gNB. The RRC message may include PC5 communication setting information. Thereby, the remote UE can receive the PC5 communication setting information with the relay UE. In the example of fig. 14, PC5 communication setting information from the remote UE to the relay UE is notified.

In step ST1410, the S-gNB may notify the remote UE of information about the settings of an adaptation layer used in communication between the relay UE and the T-gNB. This information may be included in the RRC setting change message to be notified. In this notification, the above-disclosed method of notifying the PC5 communication setting information of the remote UE from the S-gNB can be suitably applied. As the information on the setting of the adaptation layer, information on the setting of the adaptation layer between the remote UE and the relay UE and/or information on the setting of the adaptation layer between the relay UE and the T-gNB used in communication between the remote UE and the T-gNB may be notified.

In the case where the remote UE is connected to the S-gNB via the relay UE (relay UE # 1), the S-gNB may notify the remote UE of information on the setting of an adaptation layer used in communication between the remote UE and the T-gNB via the relay UE.

Thus, the remote UE can receive information on the setting of the adaptation layer used for communication between the remote UE and the T-gNB, and can perform the setting of the adaptation layer.

In step ST1411, the remote UE establishes a PC5 connection with the relay UE of the connection destination. In the PC5 connection establishment process, the remote UE notifies the relay UE of PC5 communication setting information from the remote UE to the relay UE. In the PC5 connection establishment process, the relay UE notifies the relay UE of PC5 communication setting information from the relay UE to the remote UE. Thereby, PC5 communication can be performed between the remote UE and the relay UE. In addition, data communication on the PC5 can be performed between the remote UE and the relay UE.

When an RRC message for RRC setting change from S-gNB to T-gNB is received in step ST1410, the remote UE stops communication with the S-gNB. The communication setting with the S-gNB can be released. The example of fig. 14 is not shown, but in the case where the remote UE is connected to the S-gNB via the relay UE, communication with the relay UE is stopped. The PC5 communication setting with the relay UE can be released. Thus, the remote UE can perform the PC5 connection process with the connection target relay UE and the RRC connection process with the T-gNB via the relay UE in advance.

In the case where the PC5 connection with the connection target relay UE is established in step ST1411, the remote UE may stop the communication with the S-gNB. The communication setting with the S-gNB can be released. In the case where the remote UE is connected to the S-gNB via the relay UE, communication with the relay UE may be stopped. The PC5 communication setting with the relay UE can be released. Thus, the remote UE can perform RRC connection processing with the T-gNB via the relay UE after reliably establishing the PC5 connection with the connection target relay UE.

In step ST1411, the remote UE may notify the relay UE of information regarding the settings of an adaptation layer used in communication between the remote UE and the T-gNB. In this notification, the above-disclosed notification method of setting information for PC5 communication from the remote UE to the relay UE can be suitably applied. As the information on the setting of the adaptation layer, information on the setting of the adaptation layer between the remote UE and the relay UE and/or information on the setting of the adaptation layer between the relay UE and the T-gNB used in communication between the remote UE and the T-gNB may be notified. The relay UE that receives information on the setting of the adaptation layer used in the communication between the remote UE and the T-gNB can implement the setting of the adaptation layer.

In the case where the remote UE establishes a PC5 connection with the connection target relay UE in step ST1411, the condition for stopping communication with the S-gNB may be set to a case where the remote UE is directly connected with the S-gNB. Thus, the remote UE may not perform connection processing with both the connection source relay UE and the connection target relay UE. In addition, the structure of the remote UE can be simplified. In addition, complications of HO processing for remote UEs can be avoided.

In step ST1412, the remote UE notifies the T-gNB of completion of RRC setup via the connection target relay UE. The notification may be made using RRC signaling between the remote UE and the T-gNB. An rrcrecon configuration complete message may be used. Thus, the T-gNB can identify that the remote UE has performed RRC setup and RRC connection via the relay UE. Thus, communication can be performed between the remote UE and the T-gNB via the relay UE.

The T-gNB, which has received the RRC setup complete message from the remote UE, performs path switching processing with the CN between itself and the CN in step ST 1413. Thus, a path switching process from S-gNB to T-gNB can be performed for a remote UE. In addition, the UPF of the CN can send DL data to the remote UE to the T-gNB. Thus, data communication between the remote UE and the UPF can be performed via the T-gNB and the relay UE.

The T-gNB may include information about the remote UE in a path switch request message from the CN to the AMF. May contain a path switch request message, information related to the communication of the remote UE. As the information related to the communication of the remote UE, information indicating whether or not the communication is via the relay UE may be included. Information about the relay UE may be contained. The handover request message notified to the UPF by the AMF in the CN may contain this information. In addition, the information may be included in a path switching request response message from the UPF to the AMF. Further, the information may be included in a path switching request response message from the AMF to the T-gNB. The path switching request message and the path switching request response message between the AMF and the UPF may be notified via the SMF.

In step ST1414, the T-gNB notifies the S-gNB of the release of the context of the remote UE. Thus, the S-gNB can release the context of the remote UE.

When the remote UE connects with the S-gNB via the relay UE, the S-gNB may notify the connection source relay UE of the release of the context of the remote UE in case the S-gNB receives the release of the UE context from the T-gNB. The connection source relay UE that received the notification can release the context of the remote UE. In the case where the S-gNB receives release of the UE context from the T-gNB, the connection source relay UE may be notified that communication with the remote UE is stopped. The communication stop may be notified using RRC signaling. The communication stop message may include information about the remote UE. The communication stop message may include information on a cause of the communication stop. For example, the cause information may include information indicating that the communication is stopped by HO. The relay UE that receives the communication stop message with the remote UE from the S-gNB stops relay communication between the remote UE and the S-gNB. The settings for relay communications between the remote UE and the S-gNB may be released. For example, the PC5 communication setting may be released. Thus, when the connection target relay UE of the remote UE is changed, the relay processing in the relay UE can be prevented from continuing needlessly. In addition, the relay UE can be reduced in power consumption.

After the path switching process is received, in step ST1415, data communication can be performed among the remote UE, the connection target relay UE, the T-gNB, and the CN.

Thereby, HO of a remote UE via a relay UE can be performed. In addition, the remote UE may maintain the RRC connection unchanged and change the connection target of the gNB. In addition, the communication service can be continued even when the connection destination of the gNB of the remote UE is changed.

Fig. 15 is a flowchart showing another example of a method of HO of a remote UE via a relay UE in embodiment 1. In fig. 15, steps common to those in fig. 14 are denoted by the same step numbers, and common descriptions are omitted. In the example of fig. 15, the setting method for PC5 communication between the remote UE and the relay UE is different from the example of fig. 14. In the example of fig. 15, setting information for PC5 communication between the remote UE and the relay UE is directly notified to the relay UE from the T-gNB, and setting to the remote UE is notified from the T-gNB via the S-gNB. In step ST1507, the T-gNB notifies the relay UE of the PC5 communication setting information from the remote UE to the relay UE and the PC5 communication setting information from the relay UE to the remote UE. Thus, the relay UE can receive the PC5 communication setting information from the remote UE to the relay UE and the PC5 communication setting information from the relay UE to the remote UE. In step ST1509, the T-gNB notifies the S-gNB of the PC5 communication setting information from the remote UE to the relay UE and the PC5 communication setting information from the relay UE to the remote UE. In step ST1510, the S-gNB notifies the remote UE of PC5 communication setting information from the remote UE to the relay UE and PC5 communication setting information from the relay UE to the remote UE. Thus, the remote UE can receive the PC5 communication setting information from the remote UE to the relay UE and the PC5 communication setting information from the relay UE to the remote UE.

By adopting the method as in the example of fig. 15, it is not necessary to notify the PC5 communication setting information from the connection target relay UE to the remote UE or notify the PC5 communication setting information from the remote UE to the connection target relay UE, and thus setting can be performed in advance. Further, since it is not necessary to perform communication between the connection target relay UE and the remote UE for the setting, the SRB of SL between the relay UE and the remote UE can be set. For example, setting from SRB0 of SL can be performed.

Thus, the remote UE and the relay ue#2 can acquire settings used for PC5 communication between the remote UE and the relay ue#2, and PC5 communication can be performed between the remote UE and the relay ue#2. Thus, the remote UE can connect with the T-gNB via relay ue#2, and the remote UE can communicate with the T-gNB via relay ue#2. Thus, HO of the remote UE from the S-gNB to the T-gNB can be performed. The HO from the remote UE to the indirectly connected gNB via the relay UE, in other words, the HO of the remote UE via the relay UE, becomes possible, and continuity of service can be obtained.

Modification 1 of embodiment 1.

The setting of DRBs in communication between the remote UE and the gNB via the relay UE becomes the setting via the relay UE. Then, the setting of DRBs via relay UEs is not disclosed in the above-mentioned non-patent documents 1 to 27, other documents, and the like. Therefore, there is a problem that communication between the remote UE and the gNB via the relay UE is not possible. Further, in the HO of the remote UE via the relay UE, there is no disclosure about the processing of setting of DRBs in the communication between the remote UE and the S-gNB.

In modification 1 of embodiment 1, a method for solving the above-described problem is disclosed.

In order to solve the above-described problem, in the communication system according to the present embodiment, information on setting of DRBs between the remote UE and the relay UE #1, which is used for communication between the remote UE and the S-gNB via the relay #1, is notified from the S-gNB to the T-gNB. Information about the DRB set used in communication between the remote UE and the S-gNB via relay #1 may be notified from the S-gNB to the T-gNB. Mapping information of QoS flow between the remote UE and the relay UE #1 to the DRB used in communication between the remote UE and the S-gNB via the relay #1 may be notified from the S-gNB to the T-gNB. Mapping information from QoS flow to DRB used in communication between a remote UE via relay UE #1 and S-gNB may be notified from S-gNB to T-gNB.

Information about setting of DRBs between relay UE #1 and S-gNB used in communication between a remote UE via relay #1 and S-gNB may be notified from S-gNB to T-gNB. Information about relay ue#1 and S-gNB set via DRB used in communication between remote UE of relay#1 and S-gNB may be notified from S-gNB to T-gNB. Mapping information of QoS flow between relay ue#1 and S-gNB to DRBs used in communication between a remote UE via relay#1 and the S-gNB may be notified from the S-gNB to the T-gNB.

Thus, the T-gNB can acquire information on DRB settings used in communication between the remote UE and the S-gNB via the relay UE # 1.

A method for setting DRB between a remote UE via a relay UE and a gNB is disclosed. The S-gNB may set DRBs between the remote UE and the S-gNB via relay UE # 1. The S-gNB may implement setting of DRB between the remote UE and the relay UE#1, and setting of DBR between the relay UE#1 and the S-gNB. The S-gNB may implement settings between the remote UE and the relay UE #1 and settings between the relay UE #1 and the S-gNB via the DBR between the remote UE and the S-gNB of the relay UE # 1. As the setting of DRBs between the remote UE and the gNB via the relay UE, the setting for communication from the remote UE to the S-gNB can be distinguished from the setting for communication from the S-gNB to the remote UE. The S-gNB can set the communication in each direction. The above description is referred to as S-gNB, but gNB is not particularly limited to S-gNB which is the gNB of the HO source. The present invention can be applied to a case where communication is performed between a remote UE and a gNB via a relay UE.

Thus, the S-gNB can perform settings between the remote UE and the S-gNB via the intermediate UE#1, between the remote UE and the relay UE#1, and between the relay UE#1 and the S-gNB. The settings for both may be used to set settings suitable for communication between the remote UE and the S-gNB. The S-gNB can recognize the settings of both.

Other methods are disclosed. The relay ue#1 can set DRBs for communication from the relay ue#1 to the remote UE via communication between the remote UE of the relay ue#1 and the S-gNB. The relay ue#1 can set DRBs for communication from the remote UE to the relay ue#1 via communication between the remote UE of the relay ue#1 and the S-gNB. The S-gNB sets DRB for communication between the S-gNB and the remote UE #1 via the communication between the S-gNB and the remote UE of the relay UE # 1. The above description is referred to as S-gNB, but gNB is not particularly limited to S-gNB which is the gNB of the HO source. It may be applicable to the case where communication is performed between a remote UE and a gNB via a relay UE.

Thus, the relay ue#1 and the remote UE can set the relay ue#1 in communication between the remote UE and the S-gNB via the relay ue#1. The relay ue#1 and the remote UE can be set to be suitable for communication between the remote UE and the relay ue#1, taking into consideration radio propagation conditions between the remote UE and the relay ue#1, radio resource usage conditions in each UE, and the like.

The relay UE #1 may notify the S-gNB of the setting of the DRB for communication from the relay UE #1 to the remote UE. The remote UE may notify the relay UE #1 of the setting of the DRB for communication from the remote UE to the relay UE # 1. Relay UE #1 may notify the S-gNB of the setting. Thus, the S-gNB can identify the setting between the remote UE and the relay UE #1 via the communication between the remote UE and the S-gNB of the relay UE # 1.

Thus, the S-gNB can notify the T-gNB of information on setting of DRB used in communication between the remote UE via the relay UE #1 and the S-gNB.

As information related to setting of DRBs, for example, information for identifying DRBs, setting information of each protocol stack, information of logical channels, information of RLC channels, information related to RLC bearers, and the like are available. Information on QoS flows and/or mapping information from QoS flows to DRBs may be included in the information on the setting of the DBR.

In communication between a remote UE and a gNB via a relay UE, a DRB between the remote UE and the relay UE and a DBR mapping between the relay UE and the remote UE are required in the relay UE. In a HO of a remote UE via a relay UE, information on setting of a DRB between the remote UE and the relay UE #1 and information on mapping setting of the DRB between the relay UE #1 and the S-gNB, which is used in communication between the remote UE and the S-gNB, are notified from the S-gNB to the T-gNB. The mapping method of the DRB may be set to a mapping using the identity of the DRB. Information on the mapping setting of the DRB may be set as mapping information based on the identification of the DRB. The S-gNB may notify the T-gNB of information related to the setting of the DRB disclosed above and mapping information based on the identity of the DRB.

The mapping method may be set to a mapping using the identity of the RLC channel. The information related to the mapping setting may be set as mapping information based on the identity of the RLC channel. The S-gNB may inform the T-gNB of information related to the setting of the DRB disclosed above and mapping information based on the identity of the RLC channel. The mapping method may be set to a mapping using the identity of the logical channel. The information related to the mapping setting may be set as mapping information based on the identification of the logical channel. The S-gNB may inform the T-gNB of information related to the setting of the DRB disclosed above and mapping information based on the identification of the logical channel.

The S-gNB may notify the T-gNB of the association of mapping information between the remote UE and the S-gNB from the QoS flow to the DRB and the DRB in the relay UE. The S-gNB may notify the T-gNB of the association of mapping information of the DRB from the QoS flow in the communication from the remote UE to the S-gNB and/or the communication from the S-gNB to the remote UE, and the mapping information of the DRB in the relay UE.

A method for mapping DRB between a remote UE and a relay UE and DBR between the relay UE and the remote UE in communication between the remote UE and gNB via the relay UE is disclosed. The S-gNB performs setting of DRB between the remote UE and the relay UE#1, and mapping setting between setting of DRB between the relay UE#1 and the S-gNB. The S-gNB may distinguish a mapping of DRBs for communication from the remote UE to the S-gNB from a mapping of DRBs for communication from the S-gNB to the remote UE. The S-gNB may implement mapping settings for each direction. The above description is referred to as S-gNB, but gNB is not particularly limited to S-gNB which is the gNB of the HO source. The present invention can be applied to a case where communication is performed between a remote UE and a gNB via a relay UE.

Thus, the S-gNB can implement a mapping setting adapted to the communication between the remote UE and the S-gNB. In addition, the S-gNB can identify the mapping information.

Other methods are disclosed. The relay UE #1 may implement mapping settings between the setting of DRBs between the relay UE #1 and the remote UE and the setting of DRBs between the relay UE #1 and the S-gNB via communication between the remote UE of the relay UE #1 and the S-gNB. Relay UE #1 may distinguish the mapping of DRBs for communication from the remote UE to the S-gNB from the mapping of DRBs for communication from the S-gNB to the remote UE. Relay UE #1 may implement mapping of each direction. The above description is referred to as S-gNB, but gNB is not particularly limited to S-gNB which is the gNB of the HO source. It is possible to adapt to the case of communication between a remote UE and a gNB via a relay UE.

Thus, the relay ue#1 can perform mapping setting of the mapping performed by the relay ue#1. Therefore, the mapping setting suitable for the communication between the remote UE and the S-gNB via the relay ue#1 can be set taking into consideration the radio resource usage status and the like of the relay ue#1.

The relay UE #1 notifies the S-gcb of information on setting of DRBs between the relay UE #1 and the remote UE and setting of mapping between the setting of DRBs between the relay UE #1 and the S-gcb via communication between the remote UE of the relay UE #1 and the S-gcb. Thus, the S-gNB can recognize the mapping setting.

Thus, the S-gNB can notify the T-gNB of information about the mapping setting of the DRB between the remote UE and the relay UE #1 and the DRB between the relay UE #1 and the S-gNB, which is used in the communication between the remote UE and the S-gNB.

In communication between a remote UE and a gNB via a relay UE, an adaptation layer is provided as a protocol between the relay UE and the gNB and/or between the remote UE and the relay UE (see non-patent document 27 (3 gpp TR 38.836)). In HO of communication between a remote UE and a gNB via a relay UE, an S-gNB notifies a T-gNB of information on setting of an adaptation layer between the remote UE and a relay UE #1 and/or information on setting of an adaptation layer between the relay UE #1 and the S-gNB, which is used in communication between the remote UE and the S-gNB.

The T-gNB can use information about the settings of the adaptation layer set in the communication between the remote UE and the S-gNB to implement the settings of the adaptation layer for the communication between the remote UE and the T-gNB via relay UE # 2. The T-gNB can use this information to make the adaptation layer settings in advance.

Fig. 16 is a flowchart showing an example of a method of HO of a remote UE via a relay UE in modification 1 of embodiment 1. In fig. 16, the same step numbers are given to steps common to those in fig. 14 and 15, and common descriptions are omitted. In the example of fig. 16, a method of notifying T-gNB of information on setting of DRB in communication between a remote UE and S-gNB is disclosed.

The S-gNB performs DRB setting for communication between the remote UE and relay UE #1 for communication between the remote UE and the S-gNB. In step ST1601, the S-gcb notifies the remote UE of information on DRB settings for communication between the remote UE and the relay UE #1 via the relay UE # 1. In the example of fig. 16, this information is included in the rrcrecconfiguration message between the S-gNB and the remote UE for notification. The S-gNB performs DRB setting for communication between the relay UE #1 for communication between the remote UE and the S-gNB. In step ST1602, the S-gcb notifies the relay ue#1 of information on DRB settings for communication between the remote UE and the relay ue#1. In the example of fig. 16, this information is included in the rrcrecnonfiguration message between the S-gNB and the relay UE #1 for notification. As this information, DRB information of the remote UE and the relay ue#1, DRB information between the relay ue#1 and the S-gNB, and DRB mapping information in the relay ue#1 are notified. In step ST1603, data communication is performed between the remote UE, relay ue#1, S-gNB, and UPF of CN.

In step ST1604, the S-gNB notifies the remote UE of the measurement setup via the relay ue#1. In step ST1605, the remote UE notifies the S-gNB of the measurement report via relay ue#1. The S-gNB, which decided the HO of the remote UE in step ST1405, notifies the T-gNB of the HO request message in step ST 1606. The HO request message may include information on DRB settings for communication between the remote UE and the S-gNB. As the information on DRB setting for communication between the remote UE and the S-gNB, information on DRB setting between the remote UE and the relay UE #1 for communication between the remote UE and the S-gNB, and information on DRB setting between the relay UE #1 and the S-gNB for communication between the remote UE and the S-gNB may be included. The HO request message may include mapping information of DRBs flowing from QoS to communication between the remote UE and the S-gNB. The HO request message may include DRB map information in relay ue#1. Thus, the T-gNB can identify DRB settings used in communication between the remote UE and the S-gNB via relay UE # 1. The above-described pieces of information included in the HO request message are one example of data communication setting information indicating setting contents related to data communication between the S-gNB and the remote UE.

The T-gNB uses the DRB settings notified from the S-gNB and used for communication between the remote UE via the relay UE #1 and the S-gNB to perform DRB settings used for communication between the remote UE via the relay UE #2 and the T-gNB.

In step ST1607, the T-gNB notifies the relay ue#2 of information on DRB settings used for communication between the remote UE via the relay ue#2 and the T-gNB. This information may be included in the relay request message to notify. As information on DRB settings used in communication between the remote UE and the T-gNB, information on DRB settings between the remote UE and the relay UE #2 in communication between the remote UE and the T-gNB, and information on DRB settings between the relay UE #2 and the T-gNB in communication between the remote UE and the T-gNB may be included in the relay request message. The relay request message may include mapping information of DRBs flowing from QoS to communication between the remote UE and the T-gNB. The relay request message may include DRB map information in relay ue#2. Thus, the T-gNB can notify the relay UE#2 of DRB setting for communication between the remote UE via the relay UE#2 and the T-gNB.

In step ST1609, the T-gNB notifies the S-gNB of information on DRB settings used for communication between the remote UE via the relay UE #2 and the T-gNB. This information may be included in the HO request response message to inform. As information on DRB settings for communication between the remote UE and the T-gNB, information on DRB settings between the remote UE and the relay UE #2 for communication between the remote UE and the T-gNB may be included. Thus, the S-gNB can receive DRB settings for communication between the remote UE and the T-gNB.

In step ST1610, the S-gNB notifies the remote UE of information on DRB settings used in communication between the remote UE and the T-gNB via the relay UE # 2. This information may be included in the RRC setting change message to be notified. Here, as the RRC setting change message, an rrcrecon configuration message is used. The S-gNB notifies the message via relay UE # 1. Information about DRB settings for communication between the remote UE and the T-gNB may be set as information about DRB settings between the remote UE and the relay UE #2 for communication between the remote UE and the T-gNB. Thus, the remote UE can receive DRB settings for communications between the remote UE and the T-gNB. The remote UE may use the settings to implement data communications with the T-gNB.

A method of stopping communication between a remote UE and an S-gNB is disclosed in embodiment 1, but other methods are disclosed herein. In the implementation method 1, the communication is stopped in response to the step ST1410, but here, the S-gNB notifies the remote UE of the RRC setting change message in step ST1610, and thereafter notifies the relay UE #1 of the stop of the communication with the remote UE in step ST 1611. The notification may be done using RRC signaling. The communication stop message may include information about the remote UE. The communication stop message may include information on a cause of the communication stop. For example, information indicating that the communication is stopped by HO may be included. The relay UE #1, which received the communication stop message with the remote UE from the S-gNB, stops relay communication between the remote UE and the S-gNB. The settings for relay communications between the remote UE and the S-gNB may be released. The buffer for relay communications between the remote UE and the S-gNB may be reset. The relay ue#1 can release, for example, a PC5 communication setting with the remote UE. Thus, the relay processing in the relay ue#1 can be prevented from continuing needlessly. In addition, the relay ue#1 can be reduced in power consumption.

By adopting this method, information on the setting of DRBs used in communication between the remote UE and the S-gNB can be notified from the S-gNB to the T-gNB via the relay UE # 1. The T-gNB may use this information to implement DRB setup for communications between the remote UE via relay UE #2 and the T-gNB. The setting may be notified to the remote UE and the relay UE # 2.

In the HO in the case where the remote UE is directly connected to the gNB, the remote UE starts transmission of UL data to the T-gNB after successfully RA-processing the T-gNB. However, in the case of HO of a remote UE via a relay UE, the remote UE is not directly connected with the T-gNB, and thus, there is no RA process for the T-gNB. In this case, the timing at which the remote UE starts UL data transmission to the T-gNB via the relay UE is not clear. Here, a method for solving the above-described problems is disclosed.

To solve the above problem, the remote UE starts transmission of UL data for the T-gNB via relay UE #2 after transmitting the RRC setup complete message to the T-gNB. The T-gNB can recognize that an RRC connection is made with the remote UE by receiving an RRC setup complete message from the remote UE. The T-gNB can identify that the remote UE has set an RRC setting that is notified to the remote UE from the T-gNB via the S-gNB. The T-gNB may receive UL data from the remote UE via relay UE # 2. UL data can be transmitted and received between the remote UE and the T-gNB via the relay ue#2.

Other methods are disclosed. The remote UE may start transmission of UL data after the PC5-RRC connection with relay #2 is completed. Relay UE #2 may transmit UL data received from the remote UE to the T-gNB. Thus, the remote UE can transmit UL data to the T-gNB via the relay ue#2 in advance.

Accordingly, DRB can be set in communication between the remote UE and the gNB via the relay UE. Further, communication between the remote UE and the gNB via the relay UE can be performed. Further, in the HO of the remote UE via the relay UE, the T-gNB can acquire the setting of the DRB in the communication between the remote UE and the S-gNB. Therefore, in the T-gNB, setting of DRB between the remote UE and the T-gNB using setting of DRB between the remote UE and the S-gNB can be performed. Further, in HO of a remote UE via a relay UE, for example, the following effects can be obtained: communication adapted to QoS requested by service with the continuity of service maintained, setting of DRB in T-gcb can be performed in advance, processing concerning HO can be performed with low delay, robustness of HO can be improved, and the like.

Modification 2 of embodiment 1.

In HO of a remote UE via a relay UE, reduction of data communication delay time is required. However, the method for reducing the data communication delay time in HO is not disclosed in the non-patent documents 1 to 27 and other documents.

In modification 2 of embodiment 1, a method for solving the above-described problem is disclosed.

In order to solve the above-described problem, among HO of remote UE via relay UE, DAPS (Dual Active Protocol Stack: dual active protocol stack) HO is set. Hereinafter, a DAPS HO among HO of a remote UE via a relay UE is sometimes referred to as an I-DAPS HO. Detailed methods are disclosed. In the HO of the remote UE via the relay UE, the remote UE activates a protocol stack used in both communication with the S-gNB and communication with the T-gNB. As a protocol stack for communication with the S-gNB, a protocol stack for communication between the remote UE via the relay UE #1 and the S-gNB may be used. As a protocol stack for communication with the T-gNB, a protocol stack for communication with the T-gNB by a remote UE via relay UE #2 may be used.

The I-DPAS HO may be a HO from a gcb directly connected to a remote UE to a gcb connected via a relay UE, a HO from a gcb connected to a remote UE via a relay UE to a gcb directly connected to a remote UE, or a HO from a gcb connected to a remote UE via a relay UE to a gcb connected to a relay UE. Hereinafter, they are sometimes referred to as I-DAPS HO types.

A method of setting I-DAPS HO of a remote UE via a relay UE is disclosed. The NW can set an I-DAPS HO for the remote UE. The NW can set an I-DAPS HO for the relay UE. The NW may be, for example, AMF or SMF. For example, it may be a RAN. As the RAN, for example, a gNB is possible. As gNB, S-gNB may be used, and T-gNB may be used. When the S-gNB sets, the I-DAPS HO can be set according to the communication service or the communication status of the remote UE for making the HO and the communication status of the relay UE # 1. When the T-gNB is set, it is possible to set an I-DAPS HO according to the communication service or communication status of the remote UE that is to HO the T-gNB and the communication status of the relay UE # 2.

The NW informs the remote UE of the setting of the I-DAPS HO. As the setting information of the I-DAPS HO, information indicating whether or not to set the I-DAPS HO may be included. As the setting information of the I-DAPS HO, information indicating the type of the I-DAPS HO may be included. The type of I-DAPS HO may be associated with information indicating whether or not to set. Thus, the NW can select which type of I-DAPS HO to set for the remote UE and/or the relay UE. In addition, the NW can inform the remote UE and/or relay UE which type of I-DAPS HO to perform. The remote UE and/or the relay UE can determine which type of I-DAPS HO to implement upon HO of the remote UE via the relay UE.

A notification method of I-DAPS HO setup is disclosed. The NW informs the remote UE of the I-DAPS HO setup using RRC signaling. Further, the NW notifies the relay UE of the I-DAPS HO setup by RRC signaling. As RRC signaling, for example, it may be notified with an rrcrecon configuration message. The notification method is effective in RRC connection of the remote UE or relay UE with the gNB. Further, for example, the notification may be with an RRCSetup message. In this case, the remote UE or the relay UE can be set when establishing RRC connection with the gNB, and thus can be set in advance. Further, for example, the notification may be performed with an rrcreseume message. In this case, since the setting can be performed when the remote UE or the relay UE and the gNB are in the Inactive state and transition to the RRC connected state, the setting can be performed in advance. Further, for example, the notification may be by an rrcreestablhment message. In this case, since the setting can be performed when the remote UE or the relay UE is in the RRC connected state when the RLF (Radio Link Failure: radio link failure) or the like is transferred, the setting can be performed in advance.

The T-gNB can notify the relay #2 of the I-DAPS HO setup with a relay request message.

The remote UE may inform the NW whether I-DAPS HO can be implemented. The relay UE can inform the NW whether I-DAPS HO can be implemented. The notification may be made by associating the I-DAPS HO type with information indicating whether or not it can be implemented. Information on whether or not an I-DAPS HO can be performed, or information associated with an I-DAPS HO type and information indicating whether or not it can be performed, may be set as capability information.

Disclosed is a DL transmission stop method from a relay UE #1 to a remote UE in an I-DAPS HO of the remote UE from a gNB connected via the relay UE. The S-gNB notifies the relay UE#1 of information indicating that transmission/reception between the remote UE and the S-gNB is stopped. Information indicating release of relay settings between the remote UE and the S-gNB may be notified. In the present specification, information indicating that transmission and reception between the remote UE and the S-gcb are stopped and/or information indicating that relay setting between the remote UE and the S-gcb is released is sometimes referred to as HO source relay setting release information. The S-gNB may notify relay UE #1 that HO has succeeded. The notification of this information may be performed upon the S-gNB receiving a HO success message from the T-gNB.

The relay UE #1 having received the information stops DL transmission to the remote UE. The relay UE #1 having received the information may release the setting for DL transmission to the remote UE, or may release the relay setting between the remote UE and the S-gNB.

The notification of this information by the S-gNB to relay ue#1 may be performed using RRC signaling. This information may be included in the RRC message for notification. For example, it may be included in the rrcrecon configuration message for notification. The notification may be included in an RRC message related to the relay. A message informing the relay UE #1 of whether or not the HO was successful from the S-gNB may be set and included in the message informing the relay UE #1 from the S-gNB. Thus, relay ue#1 can recognize that HO of the remote UE succeeds.

The notification of this information from the S-gNB to the relay ue#1 may be performed using MAC signaling. This information may be included in a MAC CE (Control Element) to notify. The notification of this information from the S-gNB to relay ue#1 may use L1/L2 signaling. This information may be included in the PDCCH to inform. This enables the relay ue#1 to be notified of this information from the S-gNB in advance. Further, the delay from the relay UE #1 to the stop of DL transmission to the remote UE can be reduced. In addition, unnecessary transmission/reception processing time in the relay UE #1 and the remote UE is reduced, and power consumption can be reduced.

Thus, in an I-DAPS HO of a remote UE via a relay UE, relay UE#1 can identify the HO success of the remote UE. The relay UE #1 can stop DL transmission from the relay UE #1 to the remote UE according to the success of HO of the remote UE. In addition, the relay ue#1 can release the settings used in DL transmission of the relay ue#1 and the remote UE according to the success of HO of the remote UE. Therefore, unnecessary processing such as DL transmission processing to the remote UE by the relay UE #1 can be reduced even if the remote UE successfully HO. Further, the radio resource used for this processing in the relay ue#1 can be released.

As described above, it is disclosed that the relay UE #1 having received the HO source relay setting release information stops DL transmission to the remote UE. The present invention is not limited to this, and relay UE #1 that receives the information may stop DL reception from S-gNB. The relay UE #1 receiving the information may release the setting for DL reception from the S-gNB. The relay UE #1 receiving the information may stop UL reception from the remote UE. The relay UE #1 receiving the information may release the setting for UL reception from the remote UE. The relay UE #1 receiving the information may stop UL transmission to the S-gNB. The relay UE #1 having received this information may release the setting for UL transmission to the S-gNB. Thus, the same effects as those in the above case can be obtained in each reception in the relay ue#1.

Disclosed is a DL/UL transmission/reception stopping method in a remote UE in an I-DAPS HO to the remote UE of a gNB connected via a relay UE. The T-gNB notifies the remote UE of information indicating that transmission/reception between the remote UE and the S-gNB is stopped. Information indicating a setting to release communication between the remote UE and the S-gNB may be notified. Information indicating that transmission and reception between the remote UE and the S-gcb are stopped and/or information indicating that the setting of communication between the remote UE and the S-gcb is released is sometimes referred to as HO source communication setting release information. The T-gNB may notify the remote UE of this information via relay UE # 2. The notification of this information may take place upon the T-gNB receiving the rrcrecon configuration from the remote UE.

The remote UE transceives data between the remote UE and the S-gNB until the information is received. When the remote UE receives the information, the transmission and reception of data between the remote UE and the S-gNB are stopped, and the setting for communication with the S-gNB is released.

The notification of this information from the T-gNB to the remote UE may be done using RRC signaling. This information may be included in the RRC message for notification. For example, it may be included in the rrcrecon configuration message for notification. A message indicating that the transmission and reception between the remote UE and the S-gNB is stopped or the release is set may be set and included in the message to notify the remote UE from the T-gNB. Thus, the remote UE can receive this information from the T-gNB.

The notification of this information from the T-gNB to the remote UE may be done using MAC signaling. MAC signaling from T-gNB to relay UE #2 may be used, as well as SL MAC signaling from relay UE #2 to remote UE. This information may be included in the MAC CE for notification. The notification of this information from the T-gNB to the remote UE may be done using L1/L2 signaling. This information may be included in the PDCCH from the T-gNB to the relay UE #2 and the PSCCH from the relay UE #2 to the remote UE for notification. This enables the remote UE # to be notified of the information from the T-gNB in advance. Further, the delay until transmission/reception between the remote UE and the S-gNB is stopped can be reduced. Further, unnecessary transmission/reception processing time in the remote UE is reduced, and power consumption can be reduced.

Thus, in the I-DAPS HO of the remote UE via the relay UE, the remote UE can judge that communication with the S-gNB is stopped and the setting release for the communication is performed. Therefore, wasteful processing such as communication processing between the remote UE and the S-gNB can be reduced even if the HO of the remote UE is successful. Further, the radio resource used for this processing in the relay ue#1 can be released.

A method for a remote UE to start transmission of UL data to a T-gNB in an I-DAPS HO of the remote UE via a relay UE is disclosed. When receiving information indicating to stop transmission/reception between the remote UE and the S-gNB or information indicating to release the setting of communication between the remote UE and the S-gNB from the T-gNB, the remote UE starts transmitting UL data to the T-gNB via the relay UE # 2. Thus, the remote UE can start UL data transmission to the T-gNB by stopping communication with the S-gNB or release of communication settings.

When UL data to be transmitted to the S-gcb is not acknowledged at the time of stopping communication with the S-gcb or releasing communication setting, the remote UE may transmit T-gcb sequentially from UL data to be transmitted without acknowledgement. UL data given to PDCP SNs not acknowledged for transmission may be transmitted to the T-gNB. Data following the initial UL data that was not acknowledged for transmission may be transmitted to the T-gNB. The data after the UL data given to the initial PDCP SN of the unacknowledged transmission may be transmitted to the T-gNB. Thereby, the continuity of UL data at the time of HO of the remote UE can be ensured.

Other methods are disclosed. In the case where the rrcrecon configuration complete message is transmitted to the T-gNB, the remote UE starts transmission of UL data to the T-gNB via relay UE # 2. This enables the transmission of UL data to the T-gNB to be started in advance. For example, even in the case where the remote UE does not stop communication with the S-gNB or release the communication setting, UL data transmission to the T-gNB can be started via the relay UE # 2.

When UL data for which transmission is not acknowledged exists for the S-gNB at the time when the rrcrecnonfigurationcomplete message is transmitted to the T-gNB, the remote UE can sequentially transmit the T-gNB from the UL data for which transmission is not acknowledged. The transmission method can be appropriately applied to the method disclosed above. Thus, similar to the above, the continuity of UL data at the time of HO of the remote UE can be ensured.

Fig. 17 is a flowchart showing an example of a method of I-DPAS HO in modification 2 of embodiment 1. In fig. 17, the same step numbers are given to steps common to fig. 14 and 16, and common descriptions are omitted. In step ST1701, the relay ue#1 notifies the S-gNB of the DAPS HO capability at the time of relay. May be included in the UE capability information for notification. The relay UE may notify the CN of the DAPS HO capability at the time of relay. The S-gNB may notify the CN of the DAPS HO capability at the time of relaying the ue#1. Similarly, in step ST1702, the DAPS HO capability at the time of relay is notified from the relay ue#2 to the T-gNB. In step ST1703, the remote UE notifies the S-gNB of the DAPS HO capability. Notification is via relay UE # 1. May be included in the UE capability information for notification. The remote UE may notify the CN of the DAPS HO capability at the time of relay. The S-gNB may inform the CN of the DAPS HO capability of the remote UE. The DAPS HO may be set to an I-DAPS HO. Thus, the S-gNB or CN can identify whether the remote UE or relay UE can perform DAPS HO.

In step ST1405, the S-gNB decides an I-DAPS HO for the remote UE. In step ST1706, the S-gNB notifies the T-gNB of the I-DAPS HO request. The I-DAPS HO request message may include information indicating a request for an I-DAPS HO. In step ST1707, the T-gcb notifies the relay ue#2 of the relay request. The relay request message may include information on the I-DAPS HO setting. Thus, the relay UE#2 can recognize that the I-DAPS HO is adapted to the remote UE and setting information of the I-DAPS HO.

The S-gNB, which received the HO request response from the T-gNB in step ST1609, notifies the remote UE of information about the setting of the I-DAPS HO in step ST 1710. The notification may be performed using a message for RRC setting change. The S-gNB informs the remote UE of this information via relay UE # 1. The remote UE identification receiving notification of this information indicates the implementation of the I-DAPS HO. The remote UE performs I-DAPS HO processing. The S-gNB notifies the relay UE#1 of information on the setting of the I-DAPS HO in step ST 1711. The notification may be performed using a message for RRC setting change. The relay UE #1 receiving the notification of this information recognizes that the implementation of the I-DAPS HO is instructed to the connected remote UE. Then, the I-DAPS HO process of the remote UE is performed in the relay UE#1.

In step ST1712, S-gNB determines the data transmission for T-gNB. The S-gNB may determine data transmission of buffer data held by the buffer, or may determine data transmission of DL. The S-gNB may decide to transmit buffer data and data from the UPF of the CN. In step ST1713, S-gNB transmits the SN status to T-gNB. The transmission may use Early Status Transfer (early state transmission). The SN status may include SN and/or HFN (Hyper Frame Number: super frame number) information of the original DL data transmitted to the T-gNB. After transmitting the SN status, the S-gNB transmits the data received in step ST1714 to the T-gNB. The data may be set as DL data. The S-gNB may transmit DL data that has not yet been sent to the remote UE. The S-gNB may transmit DL data received from the UPF of the CN. In step ST1715, T-gNB buffers the data from S-gNB.

The T-gNB may transmit data transmitted from the S-gNB to the relay UE #2, which is a connection target of the remote UE. Relay UE #2 may buffer data transmitted from the T-gNB. Thus, relay UE#2 can transmit data received from the T-gNB to a remote UE in advance. For example, relay ue#2 may transmit DL data received from T-gNB to the remote UE after establishment of a PC5 connection between the remote UE and relay ue#2.

The S-gNB does not stop communication to the remote UE after notifying the remote UE of the RRC setup change message including the setup information of the I-DAPS HO in step ST1710 described above. The S-gNB does not release the communication settings with the remote UE. Further, the remote UE does not stop communication with the S-gNB after receiving the message from the S-gNB in step ST1710 described above. The communication setting with the S-gNB is not released. Communication between relay UE #1 for communication with the S-gcb is not stopped. The PC5 communication setting between relay UEs for communication with the S-gNB is not released. In addition, relay ue#1 does not stop relay communication between the remote UE and the S-gNB after receiving the message for RRC setup change including the setup information of the I-DAPS HO from the S-gNB in step ST1711 described above. The relay communication setting between the remote UE and the S-gNB is not released. PC5 communication with the remote UE is not stopped. Communication with the S-gNB is not stopped. These communication settings are not released.

In step ST1721, the allocation of PDCP SNs to DL data by the S-gNB may not be stopped until an SN status is sent to the T-gNB. The S-gNB does not stop sending DL data to the remote UE until the HO success message is received. The S-gNB may not stop receiving UL data from the remote UE until the HO success message is received.

In step ST1412, the remote UE transmits an RRC setup complete message to the T-gNB. The remote UE notifies the RRC setup complete message via relay UE # 2. The remote UE, which has informed the RRC setup complete message, may start data transmission to the T-gNB. In this case, the remote UE starts data transmission via the relay UE. The T-gNB may send data received from the remote UE to the UPF.

The remote UE PC5 connected to the relay UE #2 in step ST1411 may start data transmission to the relay UE # 2. Relay UE #2 may send data received from the remote UE to the T-gNB. The T-gNB may send data received from the remote UE to the UPF. The remote UE can further advance data transmission.

The T-gNB, which received the RRC setup complete message from the remote UE, notifies the remote UE of HO source communication setup release information in step ST 1716. The T-gNB notifies the information via relay ue#2. In step ST1717, the remote UE stops transmission and reception with the S-gNB, and releases the communication setting. The T-gNB, which received the RRC setup complete message from the remote UE, notifies the S-gNB of the success of the HO in step ST 1718. The HO success message may be used in this notification. Thus, the S-gNB can recognize that the remote UE completes the RRC connection to the T-gNB through the I-DAPS HO. The S-gcb that received the HO success message from the T-gcb in step ST1718 notifies the relay UE #1 of the HO source relay setup release information in step ST 1719. The HO success message may be used in this notification. In step ST1720, relay ue#1 stops transmission and reception of relay communication between the remote UE and the S-gNB, and releases the setting for communication. Thus, the relay ue#1 can quickly stop transmission and reception of relay communication between the remote UE and the S-gNB and release the communication setting after the remote UE successfully HO. Further, the waste of the transmission/reception process of the relay ue#1 and unnecessary use of radio resources can be reduced. The relay UE #1 can be reduced in power consumption and the efficiency of use of radio resources can be improved.

In step ST1721, S-gNB transmits the SN status to T-gNB. A SN Status Transfer (SN status transmission) message may be used in this transmission. As the SN status, UL data information that needs to be retransmitted from the remote UE to the T-gNB may be included. As the SN status, DL data information newly transmitted from the T-gNB to the remote UE may be included. As the data information, PDCP SN information given to data can be set. Thus, the T-gNB can identify which data should be transceived to the remote UE.

The S-gNB transmits the data received in step ST1722 to the T-gNB. The data may be set as DL data. The S-gNB may transmit DL data that has not been transmitted to the remote UE to the T-gNB. The S-gNB may transmit DL data received from the UPF to the T-gNB.

The remote UE that completes the RRC connection with the T-gNB in step ST1412 may start data communication with the T-gNB. Alternatively, in step ST1717, the transmission/reception with the S-gNB is stopped, the setting is released, and thereafter the remote UE may start data communication with the T-gNB. In step ST1723, the remote UE starts data communication with the T-gNB via relay ue#2. Thereby, communication between the remote UE and the T-gNB can be performed.

In step ST1413, a path switching process is performed between the T-gNB and the CN, and in step ST1724, data to which an End Marker (End flag) is added is transmitted as the last data transmitted from the UPF to the T-gNB via the S-gNB. End Marker is information represented as the last data transmitted. Thus, the T-gNB can identify the last data transmitted from the S-gNB. In step ST1725, data communication is performed between the T-gNB and the UPF.

Thus, HO of the I-DAPS of the remote UE via the relay UE can be performed.

Fig. 18 is a flowchart showing another example of the method of I-DPAS HO in modification 2 of embodiment 1. In fig. 18, steps common to those in fig. 17 are denoted by the same step numbers, and common descriptions are omitted. Data communication may be performed between the remote UE and the T-gNB before transmission and reception between the remote UE and the S-gNB are stopped. This is disclosed in fig. 18.

In step ST1717 and step ST1720, before transmission/reception with the S-gNB is stopped and the setting is released, the S-gNB transmits the SN status in step ST1721, and transmits data to the T-gNB in step ST 1722. As this data, DL data may be transmitted. The S-gNB may transmit DL data that has not yet been sent to the remote UE. The S-gNB may transmit DL data received from the UPF. In step ST1723, the T-gNB transmits the data transmitted from the S-gNB to the remote UE via the relay UE # 2. Thus, data communication between the remote UE and the T-gNB can be performed in advance.

Accordingly, since the DAPS HO can be performed in the HO of the remote UE via the relay UE, the communication delay time during the HO process can be reduced. In addition, in the relay UE, unnecessary relay processing can be reduced. The relay UE can be reduced in power consumption. In addition, malfunction of the relay UE can be reduced.

Modification 3 of embodiment 1.

In I-DAPS HO of a remote UE via a relay UE, for example, if the remote UE switches all UL transmissions to T-gNB to begin transmitting UL data to T-gNB, communication with S-gNB can sometimes be problematic.

In modification 3 of embodiment 1, a method for solving the above-described problem is disclosed.

In order to solve the above-described problem, the remote UE performs UL transmission related to retransmission of communication between S-gnbs to the relay UE #1 until the communication between S-gnbs is stopped or release information of communication setting is received. In the following, 9 specific examples of UL transmissions regarding retransmissions of communications with the S-gNB are disclosed.

(11) SL L1 CSI FB (Feed Back).

(12)SL HARQ FB。

(13)SL L2 RLC FB。

(14)ROHC FB。

(15) SL HARQ data retransmission.

(16) SL RLC data retransmission.

(17) SL PDCP data retransmission.

(18) SL PDCP status report (status report) retransmission.

(19) Combinations of (11) to (18).

Thus, relay ue#1 can receive UL transmission related to retransmission of communication between the remote UE and S-gNB from the remote UE.

The relay UE #1 performs UL transmission on the S-gNB regarding retransmission of communication between the remote UE and the S-gNB until receiving transmission/reception stop information or relay setting release information between the remote UE and the S-gNB. In the following, 9 specific examples of UL transmissions related to retransmissions of communications between a remote UE and an S-gNB are disclosed.

(21)L1 CSI FB。

(22)HARQ FB。

(23)L2 RLC FB。

(24)ROHC FB。

(25) HARQ data retransmission.

(26) RLC data retransmission.

(27) PDCP data retransmission.

(28) PDCP status report (status report) retransmission.

(29) Combinations of (21) to (28).

Thus, the S-gNB can receive from the relay UE#1 an UL transmission related to retransmission of communication between the remote UE and the S-gNB.

The remote UE may continue UL transmissions on Uu regarding communications between the remote UE and the S-gNB for the S-gNB. For example, the transmission may be performed in the case of RLC retransmission between the remote UE and the S-gNB. In the following, specific examples of 4 transmissions on Uu related to communication between a remote UE and an S-gNB are disclosed.

(31)L2 RLC FB。

(32) RLC data retransmission.

(33)ROHC FB。

(34) Combinations of (31) to (33).

Thus, for example, even when RLC is retransmitted between the remote UE and the S-gNB, the S-gNB can receive UL transmission on Uu related to communication between the remote UE and the S-gNB from the remote UE.

Further, thereby, even if the remote UE starts transmitting UL data to the T-gNB, the S-gNB can receive UL transmission related to communication between the remote UE and the S-gNB from the remote UE. Thus, communication between the remote UE and the S-gNB is continued. In I-DAPS HO of remote UE via relay UE, reduction of delay time of data communication can be realized, and robustness of HO processing can be improved.

Modification 4 of embodiment 1.

In HO when UE and the gNB are directly connected, HO failure (HO failure) is managed by a timer. The timer starts when the RRC setting change is received, and stops when the RA processing is completed. When the timer expires, in other words, when RA processing is not completed in the timer, the HO fails, and RRC re-establishment is performed. However, in the HO of the remote UE via the relay UE, RA processing for the T-gNB is not performed in the case of connecting to the T-gNB via the relay UE. The processes in these cases are not disclosed in the above non-patent documents 1 to 27 and other patent documents.

Here, a method for solving the above-described problems is disclosed.

To solve the above problem, the remote UE manages HO failure with a timer. The reception of the RRC setting change from the S-gNB is started. The stopping is set to completion of the PC5-RRC connection with the relay UE. As another method, the stop may be set to complete the PC5-RRC connection with the relay UE and the RRC connection state information between the relay UE and the T-gNB is received. As another method, the stop may be set to be an RRC setting completion notification to the T-gNB. As another method, the stop may be set to the reception of the HO source communication setup release message from the T-gcb.

When the timer expires, RRC re-establishment processing may be performed on the gNB connected to the relay UE. In the case of I-DAPS HO, when the timer expires, if connected to the S-gNB, the reverse back is restored to the S-gNB setting and the SRB of the S-gNB may be activated for CP (Control Plane) signaling. As another method in the case of I-DAPS HO, when the timer expires, if the remote UE and the relay UE are not in SL RLF, and if the relay UE and the S-gNB are not in RLF, the procedure returns to S-gNB setting, and SRB of the S-gNB may be activated for CP signaling.

Thus, even when the RA processing is not performed on the T-gNB in the HO of the remote UE via the relay UE, the HO failure processing can be performed. Therefore, HO failure processing based on a radio propagation environment or the like can be performed. Further, malfunction in HO of a remote UE via a relay UE can be reduced.

Embodiment 2.

In HO of a remote UE via a relay UE, an improvement in robustness is required. As a method for improving robustness in HO, CHO (Conditional HO: conditional HO) is known (see non-patent document 19 (3 gpp ts 38.331)). However, this method is a method when the UE is directly connected to the gNB, and there is no disclosure of a case where the UE is connected to the gNB via the relay UE.

In embodiment 2, a method for improving robustness in HO of a remote UE via a relay UE is disclosed.

In order to solve the above-described problem, the communication system according to embodiment 2 sets CHO in HO of a remote UE via a relay UE. Hereinafter, CHO in HO of a remote UE via a relay UE is sometimes referred to as I-CHO. Detailed methods are disclosed. The S-gNB sets 1 or more gNBs to be candidates for HO targets. The S-gNB may set 1 or more cells composed of 1 or more gnbs serving as candidates for the HO target. The candidate cells may be cells formed by different gnbs.

The candidate cell may be a cell that can be directly connected to a remote UE. 1 or more cells that can be directly connected to a remote UE may be set as candidates for the HO target. A cell satisfying a predetermined reception quality (including received power, SINR, etc.) on DL may be a cell capable of direct connection. The predetermined DL reception quality may be determined in advance by a standard, or may be broadcasted by the gNB or notified by itself. Thus, a cell that can be connected without passing through the relay UE can be set as a candidate for the HO target. Further, the complexity of the HO process can be avoided.

The candidate cell may be a cell connected to the relay UE. Cells connected to 1 or more relay UEs may be set as candidates for the HO target. The cell to which the relay UE satisfying the predetermined reception quality in SL is connected may be a cell to which the relay UE can be connected. This makes it possible to set a cell that can be connected via the relay UE as a candidate for the HO target. Furthermore, the coverage of the cell can be extended via the relay UE.

As the candidate cell, a cell to which 1 or more relay UEs to which the remote UE has previously connected PC5 are connected may be set. Among 1 or more relay UEs to which a remote UE performs PC5 connection in advance, a cell to which a relay UE satisfying a predetermined reception quality on SL is connected may be set as a cell to which a relay UE can be connected. Thus, a cell that can be connected via a relay UE to which a remote UE has previously made a PC5 connection can be set as a candidate for the HO target. The robustness of the HO can be improved.

As a candidate cell, the above disclosed cells may be combined.

The setting of the disclosed candidate cell may be statically determined in advance by a standard or the like. Alternatively, the disclosed cell to be a candidate may be set. The S-gNB may make this setting. Alternatively, the AMF may make the setting and notify the S-gNB of the setting. By enabling the above disclosed setting of the candidate cell, flexible CHO setting can be performed according to the presence of the relay UE and the gNB, the positional relationship thereof, the radio propagation environment, and the like.

The S-gNB sets DL measurements and/or SL measurements for the remote UE. The remote UE notifies the S-gNB of the measurement result according to the setting. The S-gNB uses the DL measurement result and/or SL measurement result received from the remote UE to select 1 or more relay UEs that are candidates for the connection destination of the remote UE. The S-gNB may set the gNB to which the selected relay UE is connected as a candidate of the HO target. The S-gNB can select 1 or more cells that are candidates for HO targets.

Thus, 1 or more cells can be set as candidates for HO targets for the remote UE.

As a method of identifying the gcb to which the relay UE that is a connection target candidate of the remote UE is connected, the method disclosed in embodiment 1 can be applied appropriately to the S-gcb.

The S-gNB notifies the remote UE of HO requests to 1 or more HO target gNB (T-gNB) that become candidates. Xn signaling may be used in the notification to each T-gNB. A HO request (request) message may be used.

A signaling method in case of a T-gNB connected to a plurality of relay UEs is disclosed. A message informing each relay UE from S-gNB to T-gNB. This can notify a message for each relay UE that is a candidate for the remote UE to connect. Further, a different message may be notified to each relay UE.

As other methods, a message of each gNB is notified from S-gNB to T-gNB. Specifically, the T-gNB is notified from the S-gNB that information about 1 or more relay UEs to which the gNB is connected is included in 1 message. This reduces the amount of signaling.

The message for each cell may be notified from the S-gNB to the T-gNB. Specifically, for each cell, the T-gNB is notified from the S-gNB that information about 1 or more relay UEs to which the cell is connected is contained in 1 message. In this method, only a message corresponding to the number of cells to be targeted is notified to the T-gNB. Thereby, each cell to which the relay UE is connected can be notified of a different message.

The T-gNB of the HO target candidate notifies the relay UE that is a connection target candidate of the relay request message. Specifically, the T-gNB of the HO target candidate may notify the relay UE that is a connection target candidate of the relay request message using information on the relay UE that is a connection target candidate acquired from the S-gNB. The relay request message may include information about the remote UE to which the HO is directed. As the information about the remote UE, for example, information for identifying the remote UE, a context of the remote UE, and the like may be used. The relay request message may include setting information related to PC5 communication between the remote UE and the relay UE. Regarding notification of the relay request message, the methods disclosed in embodiment 1 and modification 1 of embodiment 1 can be applied appropriately.

The relay UE to be the connection target candidate that receives the relay request message from the T-gNB of the HO target candidate can set a relay between the remote UE to be the HO target and the T-gNB of the HO target candidate using the information included in the message. The relay UE serving as a connection target candidate notifies the T-gNB serving as the connection target candidate of the relay request response. In the case where the setting for relaying has been completed, a positive response may be notified. In the case where the setting for relaying is not completed or in the case where the setting for relaying is rejected, a negative response may be notified. The reason information may be included in the negative response. Thus, the T-gNB of the HO target candidate can recognize whether or not the relay UE serving as the connection target candidate has set a relay for the remote UE serving as the HO target.

The T-gNB of the HO target candidate notifies the S-gNB of the HO request response. The notification method of the HO request response message may be appropriately applied to the notification method of the HO request described above. The information contained in the HO request response can be appropriately applied to the information disclosed in embodiment 1.

The S-gNB may set again the T-gNB that is the candidate of the HO target. At this time, for the HO request to the T-gNB, it is possible to select from the T-gNBs that received the positive response. Thus, the S-gNB can further flexibly set the T-gNB of the HO target candidate to the remote UE in consideration of the situation of the T-gNB or the relay UE #2 connected to the T-gNB.

The S-gNB sets I-CHO execution conditions of 1 or more T-gNB to be candidates of HO targets for a remote UE performing HO. Specifically, the S-gNB notifies the remote UE of the I-CH execution condition setting. The S-gNB may perform condition setting for I-CHO of the remote UE notification T-gNB after receiving HO request responses from all T-gnbs notified of the HO request. As another method, the S-gNB may perform condition setting on I-CHO of the remote UE notification T-gNB after receiving a HO request response from a portion of the T-gnbs notified of the HO request. The notification may be performed multiple times. The S-gNB may perform correction or additional setting of the T-gNB and the I-CHO execution conditions of the T-gNB for the remote UE. The S-gcb may notify the setting until a HO success (HO success) message is received from the T-gcb.

The remote UE evaluates whether to initiate I-CHO for each T-gNB based on T-gNB and I-CHO execution conditions for the T-gNB received from the S-gNB. The reception quality of SL from the relay UE connected to the T-gNB can be used for evaluation of whether I-CHO is started. For example, the remote UE measures the reception quality of SL from the relay UE. The SL reception quality can be derived by adding a predetermined offset to the measurement result of the SL reception quality. The remote UE may activate I-CHO when the SL reception quality derived from the measurement result is better than a prescribed SL reception quality threshold.

The prescribed SL reception quality threshold and/or the prescribed offset disclosed above may be included in the setting of the I-CHO execution conditions. Measurement events for I-CHO may be set. As a measurement event for I-CHO, a predetermined SL reception quality threshold and/or a predetermined offset may be set. The setting of the execution condition of I-CHO may include an I-CHO measurement event. Thus, the remote UE can determine to which T-gNB to HO using the SL reception quality of the relay UE from the T-gNB connected to the HO target.

The remote UE performs HO via the relay UE with respect to the T-gNB to which the relay UE, which first satisfies the I-CHO start condition, among the T-gNBs of the HO target candidates is connected. Specifically, the remote UE performs PC5 connection to the relay UE that first satisfies the I-CHO activation condition among the T-gnbs of the HO target candidates. The remote UE informs the rrcrecon configuration on the T-gNB via the relay UE. Thus, the remote UE performs RRC connection to the T-gNB to which the relay UE that first satisfies the I-CHO start condition is connected.

As the setting of the I-CHO execution conditions, information relating to the I-CHO execution conditions of the T-gNB serving as the candidate of the HO target may be included. The I-CHO execution condition setting may include information on T-gNB of HO target candidates. As information on the T-gNB of the HO target candidate, information for identifying the T-gNB may be included. As information on the T-gNB of the HO target candidate, RRC setting information used in communication with the remote UE may be included.

The I-CHO execution condition setting may include information on relay UEs to which the HO target candidate T-gNB is connected. As the information about the relay UE, a setting about PC5 communication between the remote UE and the relay UE may be included. As the setting related to PC5 communication between the remote UE and the relay UE, the settings disclosed in embodiment 1 and modification 1 of embodiment 1 can be applied as appropriate. Examples of the setting include a setting for PC5 communication from the remote UE to the relay UE, a setting for PC5 communication from the relay UE to the remote UE, and/or DRB setting information between the remote UE and the relay UE. As the information related to the relay UE, information for identifying the relay UE may be included.

The S-gNB may notify the remote UE of I-CHO execution condition setting of 1 or more T-gnbs that become candidates for the HO target using RRC signaling. For example, it may be included in the rrcrecon configuration message for notification. The notification may be via relay ue#1. Since more information can be notified by using RRC signaling, for example, information on a plurality of T-gnbs serving as HO target candidates can be included. Thus, the remote UE can receive I-CHO execution condition settings of 1 or more T-gnbs that are candidates for HO targets.

The remote UE that has set the I-CHO execution condition of the T-gNB received from the S-gNB completed may notify the S-gNB of the rrcrecon configuration complete message via relay UE # 1. The S-gNB that received the message may identify that the remote UE has completed the setting of the I-CHO execution conditions of the T-gNB.

The remote UE evaluates the I-CHO execution conditions. As a result of the remote UE evaluating the I-CHO execution condition, I-CHO is initiated for the T-gNB connected to the relay UE satisfying the condition. The remote UE performs the PC5 connection processing for the relay UE satisfying the I-CHO execution condition. When a relay UE that has previously performed only a PC5 connection is set as a connection destination candidate relay UE of I-CHO, the PC5 connection process can be omitted. Thereby, shortening of the HO processing time is achieved.

The remote UE notifies the RRC setup complete message to the HO candidate T-gNB to which the relay UE is connected via the relay UE satisfying the I-CHO execution condition. An rrcrecon configuration complete message may be used. The T-gNB that received the message can identify that the remote UE has successfully made the RRC connection via relay UE # 2.

The T-gNB that completes the RRC connection with the remote UE informs the S-gNB of the success of the HO. The ho_success message may be used in the notification. The information included in the HO success message may include information on the remote UE to be HO, information indicating which relay UE to connect to, and information on PC5 communication between the remote UE and the relay UE. Thus, the S-gNB can identify when the remote UE satisfies the I-CHO execution conditions, whether the connection with the T-gNB has been completed via the relay UE.

Methods of a remote UE ceasing communication with an S-gNB via a relay UE are disclosed. In the event that a relay UE satisfying the I-CHO execution condition is detected, the remote UE may cease communication with the S-gNB. Thus, the communication process with the S-gNB can be stopped early, and the power consumption of the remote UE can be reduced.

As another method, the remote UE may stop communication with the S-gNB in case the PC5 connection is completed with the relay UE satisfying the I-CHO execution condition. This allows communication with the S-gcb to continue even when the connection with the PC5 of the relay UE fails. In the case where the PC5 connection of the remote UE and the relay UE fails, the PC5 connection process may be performed again for the same relay UE. Alternatively, in the case where the remote UE fails to connect to the PC5 of the relay UE, the I-CHO execution condition evaluation may be continued or performed again, and then the PC5 connection process may be performed with the relay UE satisfying the I-CHO execution condition. This enables the PC5 connection with the relay UE to be reliably performed.

As another approach, the remote UE may stop communicating with the S-gNB if the relay UE connection with the T-gNB is completed via the I-CHO execution condition being satisfied. The timing at which the connection with the T-gNB is judged to be completed may be a notification completion time of the rrcrecon configuration complete message. In case that the notification of the rrcrecon configuration complete message fails, the RRC setup complete message may be notified again to the same T-gNB. In the event that the notification is completed, a connection may be made with the same T-gNB. Alternatively, the I-CHO execution condition evaluation may be continued or performed again, and then the RRC setup complete message may be notified to the T-gNB via the relay UE satisfying the I-CHO execution condition. A connection can be made with the T-gNB if the notification is complete. Thus, communication with the S-gNB can be stopped after the remote UE is reliably connected to the HO target T-gNB. Further, the robustness of the HO process of the remote UE via the relay UE can be improved.

A method of stopping communication with a remote UE via a relay UE is disclosed. Upon receiving the HO success message from the T-gNB, the S-gNB stops transmitting/receiving with the remote UE via the relay UE. The settings for communication with the remote UE may be released. The method of stopping communication with a remote UE in the S-gNB can be suitably applied to the method in the I-DAPS HO disclosed in modification 2 of embodiment 1. This can stop the communication process with the S-gNB, reduce wasteful processing in the S-gNB, and reduce power consumption.

A method of relaying UE #1 to stop relay processing for communication between a remote UE and an S-gNB is disclosed. Upon receiving the HO success message from the T-gNB, the S-gNB notifies the relay UE#1 of a message for stopping transmission/reception between the remote UE and the S-gNB. As the message, a HO success message may be used. The relay UE #1 having received the message stops the transmission/reception between the remote UE and the S-gNB. The settings for communication between the remote UE and the S-gNB may be released. The relay processing stopping method between the remote UE and the S-gNB in the relay UE #1 can be suitably applied to the method in the I-DAPS HO disclosed in modification 2 of embodiment 1. This reduces unnecessary processing in the relay UE, and reduces power consumption.

A method of data transmission in I-CHO of a remote UE via a relay UE is disclosed. In the case of receiving a HO success message from the T-gNB, the S-gNB transmits an SN status to the T-gNB. A SN Status Transfer (SN status transmission) message may be used in this transmission. As the SN status, UL data information that needs to be retransmitted from the remote UE to the T-gNB may be included. As the SN status, DL data information newly transmitted from the T-gNB to the remote UE may be included. As UL data information and DL data information, PDCP SN information given data can be used. Thus, the T-gNB can identify which data should be transceived to the remote UE.

After the SN state is transmitted, the S-gNB transmits data to the T-gNB. The data may be set as DL data. In the case where the S-gNB maintains DL data that has not yet been transmitted to the remote UE, the S-gNB may transmit the DL data. The S-gNB may transmit DL data received from the UPF after transmitting the SN status.

The T-gNB transmits data transmitted from the S-gNB to the relay UE. The relay UE may be set as a relay UE of a connection destination candidate of the remote UE. The T-gNB may send data transmitted from the S-gNB to the relay UE before receiving the RRC setup complete message from the remote UE. Thus, the T-gNB can further transmit data in advance until the relay UE. Relay UE #2 may transmit data received from the T-gNB to the remote UE after completing the PC5 connection with the remote UE. Thus, the relay UE can further transmit data in advance until the remote UE. In addition, data can be further sent from the T-gNB in advance until the remote UE.

After receiving the RRC setup complete message from the remote UE, the T-gNB may send data transmitted from the S-gNB to the relay UE. The data may be transmitted via relay UE # 2. The RRC setup complete message may be set to rrcreconfigurationomple. By transmitting data between the remote UE and the T-gNB after the RRC connection is completed, data transmission from the T-gNB to the remote UE can be reliably started.

The UPF starts DL data transmission to the T-gNB through path switching processing from the S-gNB to the T-gNB between the T-gNB and the CN node. The T-gNB may send DL data from the UPF to the remote UE.

After PC5 connection is made to relay UE #2 satisfying the I-CHO execution condition, the remote UE transmits data to relay UE # 2. The remote UE may send data to relay UE #2 before sending an RRC setup complete message to the T-gNB. Thus, the remote UE can transmit data to the relay ue#2 further in advance. In the case of connection with the T-gNB, relay ue#2 may transmit data received from the remote UE to the T-gNB. Thus, relay ue#2 can transmit data to T-gNB further in advance. In addition, data can be further sent from the remote until T-gNB.

After sending the RRC setup complete message to the T-gNB, the remote UE may send data to the T-gNB. The data may be transmitted via relay UE # 2. The RRC setup complete message may be set to rrcreconfigurationomple. By transmitting data between the remote UE and the T-gNB after the RRC connection is completed, data transmission from the remote UE to the T-gNB can be reliably performed.

The S-gNB may transmit data to 1 or more T-gNBs of the HO target candidates before receiving the HO success message from the T-gNB. The trigger that the S-gNB starts data transmission before receiving the HO success message from the T-gNB may be set to a case where the S-gNB notifies the remote UE of the HO object of the I-CHO execution condition setting. The I-CHO instruction may be set as a trigger for starting data transfer, not limited to the notification of the I-CHO execution condition setting. Alternatively, the S-gNB may be set as a trigger for starting data transmission when it receives an RRC setup complete message for I-CHO execution condition setup from the remote UE.

A data transmission method before receiving a HO success message from a T-gNB is disclosed. Before receiving the HO success message from the T-gNB, the S-gNB transmits an SN status to 1 or more T-gNB of HO target candidates. SN Status Transfer (SN status transmission) may be used in this transmission. Early Status Transfer (early state transfer) may also be used. The SN status may include SN and/or HFN (Hyper Frame Number: super frame number) information of the initial DL data transmitted to the T-gNB or T-gnbs of the HO target candidates.

After the SN state is transmitted, the S-gNB transmits data to the T-gNB. As this data, DL data may be transmitted. In the case where the S-gNB maintains DL data that has not yet been transmitted to the remote UE, the S-gNB may transmit the DL data. The S-gNB may transmit DL data received from the UPF after transmitting the SN status.

The S-gNB may transmit Early STATUS Transfer (early state transmission) and data transmission to a portion of 1 or more T-gnbs of HO target candidates. For example, 2 relay UEs having a high possibility of being a connection destination in HO may be selected, and only T-gnbs connected to the 2 relay UEs may be transmitted Early STATUS Transfer (early state transmission) and data transmitted. In this case, the amount of signaling and the amount of data to be transmitted can be reduced.

Thus, the S-gNB can further transmit data to 1 or more T-gNB of the HO target candidates in advance. Therefore, when the T-gNB to which the data is transmitted becomes the HO target, the data transmission to the T-gNB is already performed, and thus the T-gNB can transmit the data to the remote UE in advance.

The S-gNB does not stop assigning PDCP SNs to DL data until the T-gNB that receives the HO success message transmits an SN status. Furthermore, the S-gNB does not stop sending DL data to the remote UE until the HO success message is received. Further, the S-gNB may not stop receiving UL data to the remote UE until the HO success message is received. Thus, transmission and reception with the S-gcb can be continued in the remote UE until the remote UE determines a relay UE satisfying the I-CHO execution condition and starts connection to the PC5 of the relay UE.

The S-gNB, which has received the HO success message from the T-gNB, notifies the T-gNB other than the T-gNB determined as the HO target of the T-gNB, which has notified the HO request message as the HO target candidate, of cancellation of the HO. For T-gNB decided as HO target, S-gNB may notify cancellation of HO target candidate cells other than the cell decided as HO target. A HO cancel message may be used in the notification.

The HO cancel message may include information on a remote UE to be HO. As the information related to the remote UE, information for identifying the remote UE may be included. The HO cancel message may include information on a T-gcb (which may be a cell) to be a target of HO cancellation. As information on the T-gNB (may be a cell), information for identifying the T-gNB (may be a cell) may be included. The HO cancel message may include information on the connection target relay UE (relay ue#2). As the information on the relay ue#2, information for the relay ue#2 may be included. The HO cancel message may include information on a T-gNB (which may be a cell) connected to the connection target relay UE (relay ue#2). As the information on the T-gNB, information for identifying the T-gNB (may be a cell) may be included.

Thus, the T-gNB serving as the HO target candidate but not the HO target and the T-gNB constituting the HO target candidate cell other than the cell determined as the HO target can recognize cancellation of the HO by receiving the HO cancel message, and release setting of the HO. Further, the HO cancellation to the relay UE disclosed later can be notified.

The T-gNB that received the HO cancellation notifies the relay UE other than the connection target relay UE (relay UE # 2) of the connection target candidate of the HO cancellation. That is, the T-gNB notifies the relay UE of the connection target candidate to which each T-gNB is connected of HO cancellation. RRC signaling may be used in the notification. A new RRC message for informing the relay UE of HO cancellation may be set. For example, the RRC message may be set as a HO cancel message.

The HO cancel message to the relay UE may include information on the remote UE to be HO. As the information related to the remote UE, information for identifying the remote UE may be included. The HO cancel message to the relay UE may include information on the T-gcb (which may be a cell) to be the HO cancel target. As information on the T-gNB (may be a cell), information for identifying the T-gNB (may be a cell) may be included. The HO cancel message to the relay UE may include information on the connection target relay UE (relay ue#2). As the information on the relay ue#2, information for identifying the relay ue#2 may be included. The HO cancel message to the relay UE may include information on the T-gNB (which may be a cell) connected to the connection target relay UE (relay ue#2). As the information on the T-gNB, information for identifying the T-gNB (may be a cell) may be included.

May contain information identifying C-IHO. That is, the relay request message for relaying the UE to the connection destination candidate in I-CHO may include information for identifying C-IHO. Further, the HO cancel message for relaying the UE to the connection destination candidate may include information for identifying the cancelled C-IHO. As this information contained in the HO cancel message, information for identifying C-IHO contained in the relay request message may be used. Thus, the connection destination candidate relay UE can identify which I-CHO is canceled from the I-CHO indicated by the information included in the HO request message received from the T-gcb.

Accordingly, the HO cancellation is notified from the T-gNB to the relay UE other than the connection target relay UE and the connection target candidate relay UE, so that the connection target candidate relay UE can receive the HO cancellation.

The relay UE receiving the connection destination candidate of the HO cancel message cancels the I-CHO setting of the remote UE. The relay UE may cancel the relay request message received from the T-gNB. The relay UE may cancel the relay setting in the relay request message received from the T-gNB. The relay UE may release information about a remote UE that is an object of HO, or a setting about PC5 communication with the remote UE.

This releases the I-CHO-related setting of the relay UE that is a candidate for connection but is not a connection destination. Further, unnecessary consumption of radio resources by the relay UE can be avoided.

FIG. 19 is a flowchart showing an example of the method of I-CHO in embodiment 2. In fig. 19, steps common to those in fig. 16 are denoted by the same step numbers, and common descriptions are omitted. In step ST1901, step ST1902, step ST1903, and step ST1933, I-CHO capabilities are notified. That is, in step ST1901, relay ue#1 notifies S-gNB of I-CHO capability. In step ST1902, relay UE#2 notifies T-gNB#1 of the capability of I-CHO. In step ST1933, relay UE#3 notifies T-gNB#2 of the capability of I-CHO. In step ST1903, the remote UE informs the S-gNB of the capabilities of I-CHO via relay UE#1. These notification methods can be appropriately applied to the method disclosed in modification 2 of embodiment 1. Thus, the S-gNB or CN can identify whether the remote UE or the relay UE is I-CHO capable.

In step ST1905, the S-gNB determines I-CHO for the remote UE. At this time, the S-gNB determines 1 or more I-CHO connection target candidate relay UEs and HO target candidates T-gNB, respectively. In step ST1906 and step ST1926, the S-gNB notifies the HO request to the T-gNB of the determined HO target candidate. In the example of fig. 19, the S-gNB determines T-gnb#1 and T-gnb#2 as HO target candidates in step ST1905, and notifies T-gnb#1 and T-gnb#2 of a HO request message in step ST1906 and step ST 1926. The message may contain information indicating that the request is CHO. In step ST1907 and step ST1927, the T-gNB serving as the HO target candidates, i.e., T-gnb#1 and T-gnb#2, notifies the relay request to the connection target candidate relay UE to which the own T-gNB is connected. Specifically, T-gnb#1 notifies relay ue#2 of the relay request message in step ST1907, and T-gnb#2 notifies relay ue#3 of the relay request message in step ST 1927. The relay request message may include information on I-CHO settings. Thus, relay ue#2 and relay ue#3 can recognize the case where CHO is applied to the remote UE and CHO setting information. In steps ST1908 and ST1928, each relay UE that is a connection destination candidate notifies the relay request response to the connected T-gNB. Relay ue#2 notifies T-gnb#1 of the relay request response, and relay ue#3 notifies T-gnb#2 of the relay request response. In step ST1909 and step ST1929, each T-gNB of the HO target candidates notifies the S-gNB of the HO request response. T-gnb#1 notifies the S-gNB of the HO request response in step ST1909, and T-gnb#2 notifies the S-gNB of the HO request response in step ST 1929. The methods of notifying the HO request message, the relay request response message, and the HO request response message are applicable to the methods disclosed in embodiment 1 and modification 1 of embodiment 1.

In step ST1910, the S-gcb that received the HO request response from each T-gcb of the HO target candidates notifies the remote UE of CHO execution condition setting. The S-gNB notifies the setting via relay ue#1. The S-gNB informs the setup with an rrcrecon configuration message through RRC signaling. As CHO execution condition settings, the message may contain the information disclosed above. For example, information on CHO connection target relay UEs, information on HO target candidates T-gNB connected to the relay UEs, information on CHO execution conditions, and the like may be included. Thus, the remote UE can evaluate CHO execution conditions.

In step ST1930, the remote UE may notify the S-gNB of the RRC setup complete message. The remote UE notifies the message via relay UE #1. Thus, the S-gNB can identify that the remote UE has performed CHO execution condition setting. In addition, the occurrence of CHO malfunction can be reduced.

The S-gNB may transmit data to 1 or more T-gNBs within the T-gNB of the HO candidate target prior to receiving the HO success message from the T-gNB. For example, data transmission may be performed for 1T-gNB. By reducing the transmission targets to 1, the amount of data to be transmitted can be reduced. In step ST1912, S-gNB decides the T-gNB of the data transmission destination. In the example of fig. 19, T-gnb#1 is determined as the data transmission target. In step ST1913, the S-gNB transmits the SN status to the T-gNB#1 of the data transmission destination. Early Status Transfer (early state transmission) may be used in this transmission. In step ST1914, the S-gNB transfers the data held by the buffer and the data from the UPF to the T-gNB #1 of the data transfer destination. The data may be set as DL data. These transmission methods can be appropriately applied to the method disclosed in modification 2 of embodiment 1. In step ST1915, the data transmitted from the S-gNB is buffered by T-gNB#1.

The T-gNB may transmit data transmitted from the S-gNB to a relay UE that is a connection target candidate for the remote UE. For example, in the example of fig. 19, T-gnb#1 may be transmitted to relay ue#2. The relay UE #2 may buffer data transmitted from the T-gNB #1. Thus, when the relay UE to which the remote UE is connected becomes relay ue#2, relay ue#2 can transmit data received from T-gnb#1 to the remote UE in advance.

In step ST1931, the remote UE evaluates CHO execution conditions. In step ST1932, the remote UE determines a relay UE satisfying the CHO execution condition as a connection target relay UE. Further, a T-gNB connected to the relay UE is determined as a HO target T-gNB. Here, relay ue#2 is determined as a connection target, and T-gnb#1 is determined as a HO target. The remote UE that decided the HO target may stop communication with the S-gNB. The settings for the communication may be released. Communication between relay UE #1 for communication with the S-gNB may be stopped. The settings for the communication may be released.

The remote UE, which determined relay ue#2 as the connection target in step ST1932, establishes a PC5 connection with relay ue#2 in step ST 1411. In step ST1916, the remote UE notifies the T-gnb#1 determined as the HO target of the HO setup change completion message via the relay ue#2. The T-gnb#1 having received the HO setting change completion message from the remote UE notifies the S-gNB of the HO success message in step ST 1718. The S-gcb notifies the relay UE #1 of HO source relay setting release information in step ST 1719. The HO success message may be used in this notification. That is, the S-gNB may include HO source relay setting release information in the HO success message and notify the relay UE #1. In step ST1720, relay ue#1 performs transmission/reception stop and release of setting between the remote UE and the S-gNB. These treatments can be appropriately applied to the method disclosed in modification 2 of embodiment 1.

The S-gNB that received the HO success message from T-gnb#1 in step ST1718 notifies the HO cancel message to the T-gNB connected to the connection target candidate relay UE that is not determined to be the connection target relay UE in step ST 1917. In the example of fig. 19, a HO cancel message is notified to T-gnb#2. In the case where data is transmitted from the S-gNB in advance, the T-gNB #2, which received the HO cancel message, may discard the transmitted data. In step ST1918, the T-gnb#2 notifies the relay ue#3, which is a relay UE serving as a connection destination candidate that is not determined as a connection destination and is connected to the T-gNB. Thus, the connection target candidate relay UE (here, relay UE # 3) that is not decided as the connection target can recognize that the remote UE is connected to another relay UE. In addition, it can be recognized that the own relay UE does not become a connection target relay UE in I-CHO. The relay ue#3 receiving the relay cancel message releases the I-CHO setting. In the case where data is transmitted from the T-gnb#2 in advance, the relay#3 that receives the relay cancel message may discard the transmitted data. This reduces unnecessary radio resource consumption in the relay ue#3 that is not the connection target.

Thus, in the HO of the remote UE via the relay UE, a plurality of connection target relay UEs can be set, and a plurality of HO targets T-gnbs can be set. In other words, I-CHO can be implemented which accompanies the communication of the remote UE and the gNB via the relay UE. In the HO of the remote UE via the relay UE, the connection target relay UE and the HO target T-gNB are decided from a plurality of options, and thus the robustness in the HO process can be improved.

Embodiment 3.

In a state where the relay UE is connected to the remote UE, the HO processing of the relay UE may be performed by the movement of the relay UE or the like. In communication between a remote UE and an NW via a relay UE, when HO of such a relay UE occurs, there is no disclosure in the above-mentioned non-patent documents 1 to 27, other documents, and the like as to how to perform connection processing between the remote UE and the NW.

In embodiment 3, a method for processing connection between a remote UE and NW accompanied by HO of a relay UE is disclosed.

In the communication system according to embodiment 3, the relay UE does not perform HO processing even when a mobile or the like occurs in the case of connecting to the remote UE. That is, the relay UE that is PC 5-connected to the remote UE may not perform HO processing. The relay UE performing the relay process of the communication between the remote UE and the gNB may not perform the HO process. When the communication quality with the gNB is deteriorated due to, for example, movement, the relay UE starts RLF (Radio Link Failure: radio Link failure). With RLF, the relay UE performs cell selection or cell reselection processing to detect a connectable cell before releasing the RRC connection with the gNB, and performs RRC establishment processing on the cell. The relay UE that fails to detect a cell within a specified timer releases the RRC connection with the gNB. The relay UE performs cell selection or cell reselection again, and performs RRC establishment processing on the detected cell to perform RRC connection. As the RRC establishment process, rrcestablisment may be performed. Thereby, the relay UE can connect with the gNB again without HO.

In the case where the relay UE performs RLF or RRC connection release, the remote UE releases the RRC connection with the gNB connected via the relay UE. The relay UE may notify the remote UE of RLF or RRC connection release with the gNB. The remote UE that receives the notification can identify that the relay UE has performed RLF or RRC connection release with the gNB. Thereby, the remote UE can release the RRC connection with the gNB connected via the relay UE.

After receiving a notification of RLF or RRC connection release with the gNB from the relay UE, the remote UE can maintain the RRC connection state for a prescribed period. Thus, when the relay UE returns to the RRC connection state with the original gcb within the predetermined period, the remote UE can maintain the connection state with the gcb. The predetermined period may be managed by a timer. As a release process of the RRC connection with the gNB connected via the relay UE, the remote UE may reset, release, and the buffer and protocol used in communication with the gNB. Thus, unnecessary consumption of radio resources in the remote UE can be avoided.

In a case where the gNB connected to the remote UE via the relay UE determines that the RRC connection with the relay UE is released, the RRC connection with the remote UE may be released. The determination of the RRC connection release with the relay UE may be performed when no communication has occurred within a predetermined period. The predetermined period may be managed by a timer. As a release process of the RRC connection with the remote UE, the gNB may reset, release a buffer, protocol used in communication with the remote UE. This can avoid wasteful consumption of radio resources in the gNB.

After the relay UE connects again with the gNB, the remote UE may apply RRC establishment processing to the gNB. The relay UE may notify the remote UE of the RRC state after establishing the RRC connection with the gNB. Thus, the remote UE can recognize whether the relay establishes an RRC connection with the gNB. Thus, the remote UE can communicate with the gNB again via the relay UE.

As a processing method of connection between a remote UE and NW accompanied by HO of a relay UE, other methods are disclosed. Even when the relay UE is connected to the remote UE, the inter-gNB HO is possible. That is, the relay UE may perform inter-gcb HO. A relay UE that is PC5 connected with a remote UE may perform HO processing. A relay UE that performs relay processing of communication between a remote UE and a gNB may perform HO processing.

Processing of a remote UE when a relay UE performs HO is disclosed. And the remote UE carries out HO on the HO target gNB of the relay UE. The remote UE may change the connected gNB to the HO target gNB of the relay UE. The remote UE may also perform HO together with the HO of the relay UE. In the case of HO of the relay UE, the remote UE may allow HO only to the HO target gNB of the relay UE. These processes may be limited to the case where the remote UE is connected to the gNB via the relay UE.

A method for a remote UE to perform HO on a HO target gNB of a relay UE is disclosed.

Fig. 20 is a flowchart showing an example of a method of a remote UE performing HO to a HO target gNB of a relay UE in embodiment 3. In step ST2001, the remote UE performs data communication with the S-gNB and CN via the relay UE.

In step ST2002, the S-gNB notifies the relay UE of the measurement setup. In step ST2003, the S-gNB receives a measurement report from the relay UE. In step ST2004, the S-gNB decides the HO of the relay UE, for example, using a measurement report from the relay UE. In step ST2005, the S-gcb notifies the T-gcb of the HO request of the relay UE. The HO request message may be used in the notification. The S-gNB may notify the T-gNB of the HO request of the remote UE together with the HO request message of the relay UE, or may include the HO request of the remote UE in the HO request message of the relay UE. Thus, the T-gNB can recognize that the HO request of the remote UE is made together with the HO request of the relay UE.

T-gNB receiving HO request of relay UE and HO request of remote UE implements permission control of relay UE and permission control of remote UE. The T-gNB performs RRC setup for the relay UE and the remote UE. In step ST2006, the T-gNB notifies the S-gNB of a HO request response message of the relay UE. The HO request response message of the relay UE may include RRC settings for the relay UE. The T-gNB notifies the HO request response of the remote UE together with or included in the HO request response message to the relay UE. The HO request response of the remote UE may include RRC settings of the remote UE.

In step ST2007, the S-gcb notifies the remote UE of an RRC message for notifying the T-gcb of an RRC setting change (may be an HO instruction). The S-gNB may notify the RRC message via the relay UE. As the RRC message, an rrcrecon configuration message may be used. The RRC message may include RRC settings for the remote UE set by the T-gNB. Thus, the remote UE can receive the RRC setting set by the T-gNB. The remote UE receiving the RRC message and implementing the RRC setup may notify the S-gNB of the rrcrecconfiguration complete in step ST 2008. The remote UE may be notified via the relay UE. Thus, the S-gNB can recognize that the RRC setting in the remote UE is implemented.

In step ST2011, the S-gNB notifies the relay UE of an RRC message for changing the RRC setting to the T-gNB. In the case where the remote UE is notified of the RRC message to the T-gNB in step ST2007 described above, the S-gNB may notify the relay UE of the RRC message. As the RRC message, rrcrecon configuration may be used. The S-gNB may include the RRC setting of the relay UE set by the T-gNB in an RRC message notified by the relay UE. Thus, the relay UE can receive the RRC setting set by the T-gNB.

The relay UE that received the notification stops communication with the S-gNB. The settings for communication with the S-gNB can be released. The relay UE that has stopped communication with the S-gNB notifies the T-gNB of the RRC setting change complete message in step ST 2013. Thus, the relay UE can notify the T-gNB of RRC setup completion. The T-gNB can recognize that the relay UE has performed RRC setup. Thereby, communication can be performed between the remote UE and the T-gNB.

The remote UE that received the RRC message for RRC setting change to the T-gNB from the S-gNB in step ST2007 described above does not immediately stop communication with the S-gNB. The remote UE may not stop communication between relay UEs for communication with the S-gNB. The remote UE that receives the RRC setting change message to the T-gNB from the S-gNB may not immediately transmit the RRC setting change complete message with the T-gNB. The RRC setting change complete message may be rrcreconfigurationomple.

The relay UE may notify the remote UE of RRC status messages with the gNB. The RRC state message with the gNB may include information indicating a change of the RRC-connected gNB. Information identifying the changed gNB may be included. Information identifying the gNB before the change may be included. The RRC state message may include RRC connection completion with the T-gNB. In step ST2014, the relay UE that has notified the completion of RRC setup with the T-gcb notifies the remote UE of an RRC state message including the completion of RRC connection with the T-gcb.

The remote UE that received the notification notifies communication with the S-gNB. The remote UE may cease communication between relay UEs for communication with the S-gNB. The settings for communication with the S-gNB can be released. The remote UE that has stopped communication with the S-gNB transmits an RRC setting change complete message to the T-gNB via the relay UE in step ST 2015. Thus, the remote UE can notify the completion of RRC setup to the HO target T-gNB of the relay UE via the relay UE. The T-gNB can identify that the remote UE has implemented RRC setup. In this way, in step ST2016, data communication can be performed between the remote UE and the T-gNB via the relay UE.

In a case where the remote UE does not perform the reception of the RRC message for the RRC setting change to the T-gNB within a predetermined time until the success of the RRC setting completion message notification to the T-gNB, for example, the remote UE may perform the HO failure processing to the T-gNB. The predetermined time may be set as a timer. When the timer is notified of success to the RRC setting complete message of the T-gNB, the remote UE resets the timer. The predetermined time may be determined statically by a standard or the like in advance, or may be notified to the remote UE from the gNB, for example, the S-gNB in advance. The notification may use RRC signaling. The timer may be set to a timer when the relay UE is connected to the gNB. May be different from the timer when directly connected to the gNB. In this case, flexible setting is possible. Alternatively, the timer when the relay UE is connected to the gNB may be the same as the timer when the relay UE is directly connected to the gNB. In this case, the processing can be simplified.

The T-gNB, which has received the RRC setup complete message from the relay UE, performs path switching processing for the relay UE between the CN and the T-gNB. This makes it possible to perform a path switching process from the S-gNB to the T-gNB for the relay UE. The UPF can send DL data to the relay UE to the T-gNB. Data communication can be performed between the relay UE and the UPF. Further, the T-gNB, which has received the RRC setup complete message from the remote UE, performs a path switching process with the CN for the remote UE. Thus, a path switching process from S-gNB to T-gNB can be performed for a remote UE. The UPF can send DL data to the remote UE to the T-gNB. Data communication can be performed between the remote UE and the UPF.

Other methods of path switching processing are disclosed. In the case of receiving RRC setup complete messages from the relay UE and the remote UE, the T-gNB may implement path switching processing for the relay UE and the remote UE between itself and the CN. In this case, the T-gNB may include information about communication of the relay UE and information about communication of the remote UE in a path switching request message to the AMF. The AMF may include information related to communication of the relay UE and information related to communication of the remote UE in a path switch request message to the UPF. Further, information about the communication of the relay UE and the communication of the remote UE may be included in a path switching request response message from the UPF to the AMF. Further, information related to communication of the relay UE and information related to communication of the remote UE may be included in a path switching request response message from the AMF to the T-gNB. The T-gNB informs the S-gNB of the release of the relay UE 'S context and the release of the remote UE' S context. They may be included in the same message for notification. Thus, the S-gNB can release the context of the relay UE and can release the context of the remote UE.

Thus, the UPF can perform a path switching process to the T-gNB for both the communication of the relay UE and the communication of the remote UE. In addition, the UPF can send DL data to the relay UE and the remote UE for the T-gNB. In addition, data communication can be performed between the relay UE and the UPF, and data communication can be performed between the remote UE and the UPF. In addition, the amount of signaling can be reduced.

In the example of fig. 20, a method of implementing a path switching process for a relay UE and a remote UE between a T-gNB and a CN upon receiving RRC setup complete messages from the relay UE and the remote UE is disclosed. Specifically, in step ST2017, the T-gNB performs a path switching process with the CN. Thus, path switching between the relay UE and the remote UE can be performed. In step ST2019, data communication between the remote UE and the T-gNB or CN is enabled via the relay UE. In step ST2018, the T-gNB notifies the S-gNB of the UE context release of the relay UE and the remote UE. Thereby, UE context release for both relay UE and remote UE can be implemented.

The S-gNB can perform data transmission processing of communication between the remote UE and the UPF on the T-gNB by performing the RRC setting change notification to the T-gNB on the remote UE or performing the later party of the RRC setting change notification to the T-gNB on the relay UE. In addition, the S-gNB may perform data transmission processing for relaying communication (if any) between the UE and the UPF for the T-gNB.

As another method, the S-gNB may perform data transfer processing of communication between the remote UE and the UPF on the T-gNB by performing an earlier one of RRC setting change notification to the T-gNB or RRC setting change notification to the T-gNB on the remote UE. In addition, the S-gNB may perform data transmission processing for relaying communication (if any) between the UE and the UPF for the T-gNB. The method can also be applied in the case where the remote UE performs HO to the HO target gNB of the relay UE. Thus, the data transmission process of the communication between the remote UE and the UPF and the data transmission process of the communication (if any) between the relay UE and the UPF can be performed to the T-gNB in advance.

As another method, the S-gNB may implement RRC setup change notification to the T-gNB for the remote UE to perform data transmission processing of communications between the remote UE and the UPF for the T-gNB, and the S-gNB may implement RRC setup change notification to the T-gNB for the relay UE to perform data transmission processing of communications (if any) between the relay UE and the UPF for the T-gNB. The S-gNB may also transmit data received from the UPF. Thus, the data transmission processing of the communication between the remote UE and the UPF can be performed on the T-gNB in advance. Further, since the transmission is performed at each individual timing, malfunction can be reduced.

In the case of fig. 20, in step ST2009, S-gNB transmits the SN status to T-gNB. The SN status may be transmitted using SN Status Transfer (SN status transmission). In step ST2010, the S-gNB transmits data to the T-gNB.

In step ST2012, the data transmitted from the S-gNB is buffered by the T-gNB. The T-gNB starts transmission and reception of DL data and/or UL data with the remote UE, triggered by the reception of the RRC setting completion message from the remote UE or the reception of the RRC setting completion message from the remote UE. In the example of fig. 20, the reception of the RRC setup complete message from the remote UE in step ST2015 becomes a trigger, and the T-gNB starts data transmission and reception with the remote UE in step ST 2016. After starting data transceiving, the T-gNB may transmit the buffered data. Thus, data can be transmitted and received between the remote UE and the T-gNB via the relay UE.

Before the relay UE notifies the RRC setting change, the S-gNB notifies the remote UE of the RRC setting change, and performs SN status transmission and data transmission to the T-gNB in the notification of the RRC setting change by the S-gNB to the relay UE, and in this case, the S-gNB may perform transmission and reception of DL data and/or UL data with the remote UE to and from the relay UE until data transmission is performed. The relay UE may transmit and receive the DL data and/or UL data to and from the remote UE.

Upon receiving the RRC setting change from the S-gNB, the relay UE may stop DL data transmission to the remote UE. Thus, the relay UE may not transmit feedback information such as PDCP Status report (PDCP status report) for DL data transmission to the remote UE to the S-gNB. That is, the feedback process can be simplified. Further, processing in the relay UE can be reduced.

Upon receiving the RRC setting change from the S-gNB, the relay UE may stop UL data reception from the remote UE. As another method, in the case where the RRC setting change is received from the S-gNB, the relay UE may continue UL data reception from the remote UE. The relay UE may buffer UL data received from the remote UE in the HO. After the RRC setup completion notification to the T-gNB, the relay UE transmits UL data received from the remote UE to the T-gNB. This can shorten the delay time until UL data can be transmitted from the remote UE to the T-gNB.

In the case of a relay UE making a DAPS HO, a DAPS HO of a remote UE may follow. The remote UE may activate a protocol stack for both communication with the S-gNB and communication with the T-gNB via the relay UE. The method disclosed in modification 2 of embodiment 1 can be applied appropriately to DAPS HO of a remote UE via a relay UE.

Other methods of remote UE implementing HO to the HO target gNB of relay UE are disclosed. In this other method, after the completion of the HO of the relay UE, the HO of the remote UE is performed.

Fig. 21 is a flowchart showing another example of a method of the remote UE performing HO to the HO target gNB of the relay UE in embodiment 3. In the example of fig. 21, a method of implementing HO of a remote UE after HO of a relay UE is completed is disclosed. In fig. 21, steps common to those in fig. 20 are denoted by the same step numbers, and common descriptions are omitted.

In step ST2006, the S-gcb that received the HO request response message from the T-gcb notifies the relay UE of the RRC setting change message in step ST2011, and performs HO of the relay UE. In step ST2011 and subsequent steps ST2009 to ST2013, HO of the relay UE is performed. In step ST2013, the T-gNB, which received the RRC setting complete message from the relay UE, notifies the remote UE of the RRC setting change message in step ST 2101. The message may be notified via the relay UE. Thus, the remote UE can implement RRC settings for communications between the remote UE and the T-gNB, which are set by the T-gNB. The remote UE performs RRC setting based on the RRC setting change message received from the T-gNB, and notifies the T-gNB of an RRC setting completion message in step ST 2015. The message may be notified via the relay UE. Thus, the T-gNB can recognize that the remote UE has completed RRC setup, and can recognize that communication has become possible.

Thus, the HO of the remote UE is performed after the completion of the HO of the relay UE, and thus, it is possible to avoid a situation in which the timing of performing the HO processing in the remote UE and the relay UE becomes complicated. Therefore, malfunction of the HO process can be reduced, and robustness of the HO process can be improved.

Other methods of remote UE implementing HO to the HO target gNB of relay UE are disclosed. In this other method, the relay UE notifies the remote UE of RRC settings of the T-gNB.

Fig. 22 is a flowchart showing another example of a method of the remote UE performing HO to the HO target gNB of the relay UE in embodiment 3. In the example of fig. 22, a method of the relay UE informing the remote UE of RRC setup of the T-gNB is disclosed. In fig. 22, the steps common to fig. 20 are denoted by the same step numbers, and common descriptions are omitted.

The S-gcb that received the HO request response message from the T-gcb in step ST2006 notifies the relay UE of the RRC setting change message in step ST 2201. Information on the RRC setting for communication with the T-gNB of the remote UE is included in the RRC setting change message. The relay UE that received the RRC setting change message stops communication with the S-gNB. The communication setting with the S-gNB can be released. The relay UE also performs RRC setting for communication with the T-gNB.

In step ST2202, the relay UE notifies the remote UE of an RRC setting change message. Information on RRC settings for communication with the T-gNB may be included in the message. Thus, the remote UE can receive information on RRC settings for communication with the T-gNB. The remote UE, which has received information on the RRC settings for communication with the T-gNB, stops communication with the S-gNB. The communication setting with the S-gNB can be released. The remote UE performs RRC setting for communication with the T-gNB.

In step ST2203, the remote UE notifies the relay UE that RRC setup for communication with the T-gNB is completed. The RRC setup complete message may be used in the notification. In step ST2204, the relay UE notifies the T-gNB of the RRC setup complete message. The message may include completion of RRC setup for communication with the T-gNB in the relay UE and completion of RRC setup for communication with the T-gNB in the remote UE. Thus, the T-gNB can recognize that RRC setup is completed in the relay UE, and can recognize that RRC setup is completed in the remote UE. Thus, the T-gNB can identify that communication with a remote UE can be via a relay UE. In step ST2016, the remote UE can communicate with the T-gNB via the relay UE.

Thus, the relay UE notifies the remote UE of the RRC setting for communication with the T-gNB, and the remote UE can perform HO on the T-gNB. In addition, communication of an RRC message from the T-gNB to the remote UE is not required, and thus the amount of signaling can be reduced.

Thereby, the remote UE can perform HO to the HO target gNB of the relay UE. Even when a relay UE connected to a remote UE performs HO, continuity of communication service between the remote UE and NW can be ensured.

It is possible to set whether or not a relay UE in connection with a remote UE can perform HO. The CN may implement the setting. For example, the RAN node is notified of the HO-capable setting from the CN node. The CN node or the RAN node may notify the relay UE of the HO-capable setting. The CN node may be an AMF. Alternatively, the RAN may implement the HO-capable setting. For example, the setting of whether or not to enable HO may be performed from the RAN node to the relay UE. Accordingly, whether or not the relay UE connected to the remote UE can perform HO can be set according to the radio propagation state, the processing load in the relay UE, and the like. If the HO is negative, the relay UE performing the relay process of the communication between the remote UE and the gNB does not perform the HO process. In case HO is allowed, the remote UE performs HO to the HO target gNB of the relay UE. This makes it possible to perform optimal connection processing between the remote UE and NW in association with HO of the relay UE, based on radio propagation conditions, processing load in the relay UE, and the like.

Embodiment 4.

Robustness in the connection of remote UEs and the gNB via relay UEs is required. Conventionally, in order to improve robustness in direct connection between a UE and a gNB, for example, the following methods have been disclosed: when an RRC re-establishment request message (rrcreestabilishmentrequest) is notified from the UE to the gNB, the UE transmits an identity of the last connected cell. However, in the case where the remote UE is connected to the gNB via the UE, this method cannot be applied since the remote UE is directly connected to the relay UE, not directly connected to the cell.

In embodiment 4, a method of improving robustness in connection between a remote UE and a gNB via a relay UE is disclosed.

In the communication system according to the present embodiment, when establishing or re-establishing an RRC connection with a gNB via a relay UE, a remote UE notifies the gNB of an RRC re-establishment request message via the relay UE. The RRC re-establishment request message includes information on the relay UE connected last time. As the information about the relay UE, information for identifying the relay UE may be used. The RRC re-establishment request message may include information on the gcb to which the relay UE connected last time is connected. As the information about the gNB, information for identifying the gNB may be used.

Thus, the gNB connected to the remote UE via the relay UE can identify the relay UE to which the remote UE was last connected.

In a case where the remote UE establishes or re-establishes an RRC connection with the gNB without via the relay UE, the RRC re-establishment request message is notified to the gNB. The RRC re-establishment request message includes information on the relay UE connected last time. As the information about the relay UE, information for identifying the relay UE may be used. The RRC re-establishment request message may include information on the gcb to which the relay UE connected last time is connected. As the information about the gNB, information for identifying the gNB may be used.

Thus, the gNB connected to the remote UE can identify the relay UE to which the remote UE was last connected.

The relay UEs connected last time are not limited to 1, and may be plural. The maximum number may be determined statically using criteria or the like. Malfunction can be reduced and setting processing can be simplified.

The gNB may use information received from the remote UE regarding the relay UE that was last connected and/or information regarding the gNB to make a setup, for example, for the remote UE to measure the relay UE.

This reduces the release of the RRC connection due to RLF or the like. Further, the continuity of communication service between the remote UE and the gNB via the relay UE can be further improved.

Embodiment 5.

Conventionally, when a UE is directly connected to a gNB, the gNB provides an identifier to the UE, and the identifier is used to identify the UE in direct communication between the UE and the gNB. However, in communication between the remote UE and the gNB via the relay UE, direct communication is not performed in the remote UE and the gNB. Therefore, how to identify each other UE, or how to identify remote UE by the gNB, becomes a problem. The identification of the UE used for communication between the remote UE and the gNB via the relay UE is not disclosed in the above-mentioned non-patent documents 1 to 27, other documents, and the like.

In embodiment 5, a method for solving such a problem is disclosed.

In order to solve the above-described problem, in the communication system according to the present embodiment, when the PC5 connection between the remote UE and the relay UE is established in the communication between the remote UE and the gNB via the relay UE, a default value is used as the destination L2ID (Destination Layer-2 ID). In the discovery process for searching for the relay UE, as the destination L2ID, a default value may be used. The default value may be used for communication from the remote UE to the relayed PC 5. The default value may also be used for communication from the relay UE to the remote PC 5. Default values may also be used for bi-directional PC5 communications.

A default destination L2ID may be set for relaying. A default destination L2ID may be set for U2N relay. A default destination L2ID may be set for U2U relay. A default destination L2ID may be additionally set for U2N relay. The destination L2ID may be associated with a service type. As the service type, it is possible to set for the relay. The UE derives the destination L2ID from the service type. For example, when the service type is relay, the UE uses a default destination L2ID for relay.

The destination L2ID may be associated with an application layer ID. The UE may associate the destination L2ID with the application layer ID.

In communication between a remote UE and a gNB via a relay UE, when a PC5 connection between the remote UE and the relay UE is established, the UE itself may allocate a transmission source L2ID (source Layer-2 ID). In the discovery process, the UE itself may allocate a transmission source L2ID. The transmission source L2ID may be associated with an application layer ID. The UE may associate them.

The gNB assigns a UE identity to a remote UE connected via a relay UE. The gNB may assign a UE identity for each cell to the remote UE. The UE identity may be a C-RNTI. Other RNTIs are also possible. The gNB informs the remote UE of the UE identity allocated to the remote UE via the relay UE.

The gNB notifies the remote UE of a UE identity assigned to the remote UE using RRC signaling between the remote UE and the gNB via the relay UE. The gNB may notify the remote UE of the UE identity in an RRC connection establishment process, such as an RRC setup process, performed between the relay UE and the remote UE. gNb may include the UE identity in an RRCSetup message to inform the remote UE. The gNB may notify the remote UE of the UE identity in the RRC setting change process performed between the relay UE and the remote UE. The gNB may include the UE identity in the RRCRECONfigure message for notification. The gNB may notify the remote UE of the UE identity in an RRC connection state transition process between an Inactive (Inactive) state and an Active (Active) state, which is performed between the relay UE and the remote UE. The gNB may include the UE identity in a RRCResume message for notification.

The gNB may notify the remote UE of the UE identity assigned to the remote UE using MAC signaling between the remote UE via the relay UE. The gNB may include the UE identity in the MAC CE to inform.

Thus, the gNB can notify the remote UE of the UE identity assigned to the remote UE. The remote UE can receive a UE identity from the gNB. The remote UE can use the UE identity received from the gNB in communication with the gNB via the relay UE.

For example, the gNB may include the UE identity assigned to the remote UE in an RRC message to the remote UE. The remote UE can identify the RRC message to itself by receiving the UE identity. When the relay UE receives an RRC message from the gNB to the remote UE, the relay UE can identify which remote UE the RRC message is to by receiving the UE identity. The relay UE can relay the RRC message to the remote UE.

For example, the UE identity assigned to the remote UE may be included in an RRC message from the remote UE to the gNB. The gNB can recognize which UE the RRC message originated from by receiving the UE identity. When the relay UE receives an RRC message from the remote UE to the gNB, the relay UE can recognize which remote UE the RRC message is from by receiving the UE identity. The relay UE can relay the RRC message to the gNB.

For example, the gNB may include the UE identity assigned to the remote UE in MAC signaling to the remote UE. The gNB may include the UE identity in the MAC CE as MAC signaling. The remote UE can identify the MAC signaling to itself by receiving the UE identity. When the relay UE receives MAC signaling from the gNB to the remote UE, the relay UE can identify which remote UE to send the MAC signaling to by receiving the UE identification. The relay UE can relay the MAC signaling to the remote UE.

For example, the UE identity assigned to the remote UE may be included in MAC signaling from the remote UE to the gNB. The gNB may include the UE identity in the MAC CE as MAC signaling. The gNB can recognize from which UE the MAC signaling comes by receiving the UE identity. When the relay UE receives MAC signaling from the remote UE to the gNB, the relay UE can recognize from which remote UE the MAC signaling comes by receiving the UE identification. The relay UE can relay the MAC signaling to the gNB.

Thus, in communication between the remote UE and the gNB via the relay UE, communication for determining the remote UE can be performed.

An allocation and notification method of UE identities in HO is disclosed. The T-gNB allocates a UE identity for use in communication with a remote UE of the HO object to the remote UE. The T-gNB informs the remote UE of the assigned UE identity via the S-gNB. In the case where the remote UE is connected to the S-gNB via the relay UE, the T-gNB may notify the remote UE of the allocated UE identity via the S-gNB, the relay UE.

Xn signaling may be used in the notification of the UE identity from the T-gNB to the S-gNB. For example, the UE identity may be included in a HO Request response (HO Request Ack) message for notification. RRC signaling may be used in the notification of this UE identity from the S-gNB to the remote UE. For example, the UE identity may be notified contained in an RRC setting change (may be rrcrecon configuration) message. MAC signaling may be used in the notification of this UE identity from the S-gNB to the remote UE.

Thus, the remote UE can acquire in advance the UE identity allocated by the T-gNB of the HO target. The UE identity can be used in advance in the communication between the remote UE and the T-gNB.

The UE identity allocated to the remote UE may be a SL-RNTI. The SL-RNTI may be used in the communication between the remote UE and the gNB.

As other methods, the gNB may assign the SL-RNTI to the remote UE separately from the UE identity of the remote UE disclosed above, i.e., the C-RNTI. The gNB may assign multiple UE identities to the remote UE. The gNB informs the remote UE of the assigned plurality of UE identities. For example, the C-RNTI may be used in communication between a remote UE and the gNB, and the SL-RNTI may be used in communication between the remote UE and the relay UE.

Thus, the UE identity can be flexibly utilized in communication between the remote UE and the gNB.

Thus, in communication between a remote UE via a relay UE and the gNB, the gNB can provide an identification to the UE. In the existing direct communication between the remote UE and the gNB, the UE identity is notified from the gNB to the remote UE in the RA process. However, even in the case where RA processing is not performed in communication between a remote UE via a relay UE and the gNB, by adopting this method, the gNB can provide the UE with the UE identity. Thus, in this communication, in order to determine the remote UE, the identity of the remote UE provided by the gNB can be used. Further, since the remote UE can be specified, malfunction in communication between the remote UE and the gNB via the relay UE can be reduced.

In the present specification, the description is given of "gNB or cell", but unless otherwise stated, the description may be given by way of gcb or cell. For example, although the HO between the gmbs is described, the HO between the cells may be also described. The HO between the cell composed of S-gNB and the cell composed of T-gNB can be obtained. The S-gNB and the T-gNB may be the same or different. As the case where the S-gNB is the same as the T-gNB, for example, HO between different cells constituted by the same gNB may be used. In the case where the S-gNB is the same as the T-gNB, for example, the processing between the S-gNB and the T-gNB disclosed in the present specification may be deleted.

As the case where the S-gNB is the same as the T-gNB, for example, the method disclosed in the present specification can be suitably applied to a handover process to/from indirect communication between a remote UE via a relay UE and the gNB. For example, the present invention can be suitably applied to a handover process from direct communication of a remote UE and a gNB to communication (indirect communication) of the remote UE and the gNB via a relay UE. For example, the handover processing from communication (indirect communication) of a remote UE and a gNB via a relay UE to direct communication of the remote UE and the gNB may be suitably applied.

In the present specification, the case of communication between the remote UE and the gNB via 1 relay UE is described, but the method disclosed in the present specification may be applied appropriately to the case of communication between the remote UE and the gNB via a plurality of relay UEs. For example, in the case where the remote UE and the gNB communicate via 2 relay UEs of the relay ue#21 and the relay ue#22, the above-disclosed method can be suitably applied to a PC connection between the remote UE and the relay ue#21, a PC connection between the relay ue#21 and the relay ue#22, and a Uu connection between the relay ue#22 and the gNB. For example, in the method disclosed in embodiment 1, when the remote UE is connected to the T-gNB via the relay ue#21 and the relay ue#22, the T-gNB may notify the remote UE of settings used for the PC connection between the remote UE and the relay ue#21 and settings used for the PC connection between the relay ue#21 and the relay ue#22 via the S-gNB. The remote UE may notify the relay UE #21 of a part or all of the setting. The relay ue#21 may notify part or all of the setting to the relay ue#22. This can achieve the same effect even when communication is performed between the remote UE and the gNB via a plurality of relay UEs.

In the present disclosure, a UE that generates service data is set as UE-TX, and a UE that receives service data is set as UE-RX. For example, in the case where UE-TX is set as UE1 and UE-RX is set as UE2, when service data is generated in UE2 and data is transmitted to UE1, the method of the present disclosure may be applied with UE2 set as UE-TX and UE1 set as UE-RX. Thus, the same effect can be obtained.

The above embodiments and modifications are merely examples, and the embodiments and modifications can be freely combined. Further, any constituent elements of the respective embodiments and modifications thereof may be appropriately changed or omitted.

For example, in the above embodiments and modifications thereof, a subframe is an example of a time unit of communication in the 5 th generation communication system. A subframe may be a scheduling unit. In the above embodiments and modifications thereof, the processing described in subframe units may be performed in TTI units, slot units, sub-slot units, and minislot units.

For example, the methods disclosed in the above embodiments and modifications thereof are not limited to V2X (Vehicle-to-everything) services, and may be applied to services using SL communication. For example, the present invention can be applied to SL communication used for various services such as a proxy service (Proximity-based service), public security (Public security), wearable inter-terminal communication, and inter-device communication in a factory.

The present disclosure has been described in detail, but the foregoing description is in all aspects only illustrative and not restrictive. It is understood that numerous modifications not illustrated can be envisaged.

Description of the reference numerals

200. 210 communication system

202 communication terminal device (Mobile terminal)

203. 207, 213, 217, 223-1, 224-2, 226-1, 226-2, 750 base station device (base station)

204MME/S-GW (MME)

204a MME

214AMF/SMF/UPF section (5 GC section)

218. Central unit

219. Dispersing unit

301. 403 protocol processing unit

302. Application part

303. 404 transmit data buffer

304. 405 coding part

305. 406 modulation part

306. 407 frequency conversion unit

307-1 to 307-4, 408-1 to 408-4 antennas

308. 409 demodulation unit

309. 410 decoding section

310. 411, 506, 526 control part

401 EPC communication unit

402. Other base station communication unit

412 5GC communication section

501PDN GW communication part

502. 522 base station communication unit

503. 523 user plane communication unit

504HeNBGW communication unit

505. 525 control plane control unit

505-1, 525-1NAS Security portion

505-2SAE bearer control part

505-3, 525-3 idle state mobility management section

521 data network communication unit

525-2PDU session control unit

527 session management section

751-1 to 751-8 beams.

Claims

1. A communication system, comprising:

A 1 st base station, the 1 st base station being connected to a 1 st communication terminal, the 1 st communication terminal supporting inter-terminal communication in which communication terminals directly communicate with each other; and

a 2 nd base station, the 2 nd base station being connected to a 2 nd communication terminal, the 2 nd communication terminal supporting the inter-terminal communication,

when a request for switching the 1 st communication terminal to connect to the base station via the 2 nd communication terminal is received, the 2 nd base station transmits communication setting information indicating setting contents for inter-terminal communication between the 1 st communication terminal and the 2 nd communication terminal to the 1 st communication terminal and the 2 nd communication terminal.

2. The communication system of claim 1, wherein,

the 2 nd base station transmits the communication setting information to the 1 st communication terminal via the 1 st base station, and directly transmits the communication setting information to the 2 nd communication terminal.

3. The communication system of claim 1, wherein,

the communication setting information includes: 1 st setting information indicating setting contents related to communication in a direction from the 1 st communication terminal to the 2 nd communication terminal; and 2 nd setting information indicating setting contents concerning communication in a direction from the 2 nd communication terminal toward the 1 st communication terminal,

The 2 nd base station transmits the 1 st setting information to the 1 st communication terminal via the 1 st base station and directly transmits the 2 nd setting information to the 2 nd communication terminal,

the 1 st communication terminal acquires the 2 nd setting information from the 2 nd communication terminal,

the 2 nd communication terminal acquires the 1 st setting information from the 1 st communication terminal.

4. A communication system as claimed in any one of claims 1 to 3, characterized in that,

the 1 st communication terminal is connected to the 1 st base station via a 3 rd communication terminal supporting the inter-terminal communication,

in the case where a handover is performed for the 1 st communication terminal to connect to the 2 nd base station via the 2 nd communication terminal, the 1 st base station transmits setting information for data communication indicating setting contents concerning data communication with the 1 st communication terminal to the 2 nd base station.

5. The communication system of claim 4, wherein,

when the 3 rd communication terminal performs a handover and switches a connection destination, the 1 st communication terminal switches the connection destination to a base station of the handover destination of the 3 rd communication terminal.

6. A communication system as claimed in any one of claims 1 to 4, characterized in that,

The handover is set to a dual active protocol stack (DualActive Protocol Stack) handover.

7. A communication system as claimed in any one of claims 1 to 4, characterized in that,

the switching is set to Conditional (Conditional) switching.

8. A base station for a mobile communication system,

can be connected to a communication terminal supporting inter-terminal communication in which communication terminals directly communicate with each other, the base station being characterized in that,

when a request for switching a 1 st communication terminal, which is a communication terminal connected to another base station, to the base station via a 2 nd communication terminal, which is a communication terminal connected to the base station, is received, communication setting information indicating setting contents for performing inter-terminal communication between the 1 st communication terminal and the 2 nd communication terminal is transmitted to the 1 st communication terminal and the 2 nd communication terminal.